diff --git a/checker/collect.go b/checker/collect.go
index 8db0ddb..d576fb3 100644
--- a/checker/collect.go
+++ b/checker/collect.go
@@ -22,6 +22,7 @@ func (p *tlsProvider) Collect(ctx context.Context, opts sdk.CheckerOptions) (any
 		timeoutMs = DefaultProbeTimeoutMs
 	}
 	timeout := time.Duration(timeoutMs) * time.Millisecond
+	enumerate := sdk.GetBoolOption(opts, OptionEnumerateCiphers, false)
 
 	entries, warnings := contract.ParseEntries(raw)
 	for _, w := range warnings {
@@ -40,15 +41,36 @@ func (p *tlsProvider) Collect(ctx context.Context, opts sdk.CheckerOptions) (any
 	var mu sync.Mutex
 	var wg sync.WaitGroup
 	sem := make(chan struct{}, MaxConcurrentProbes)
+dispatch:
 	for _, e := range entries {
+		select {
+		case sem <- struct{}{}:
+		case <-ctx.Done():
+			break dispatch
+		}
 		wg.Add(1)
-		sem <- struct{}{}
 		go func() {
 			defer wg.Done()
 			defer func() { <-sem }()
 			pr := probe(ctx, e.Endpoint, timeout)
 			log.Printf("checker-tls: %s %s:%d → tls=%s handshake_ok=%t elapsed=%dms err=%q",
 				pr.Type, pr.Host, pr.Port, pr.TLSVersion, pr.TLSHandshakeOK, pr.ElapsedMS, pr.Error)
+			if enumerate && pr.TLSHandshakeOK {
+				enumRes, skipReason := enumerateEndpoint(ctx, e.Endpoint, enumerationBudget)
+				switch {
+				case enumRes != nil && enumRes.Skipped != "":
+					pr.Enum = enumRes
+					log.Printf("checker-tls: enum %s:%d → error: %s (duration=%dms)",
+						pr.Host, pr.Port, enumRes.Skipped, enumRes.DurationMS)
+				case enumRes != nil:
+					pr.Enum = enumRes
+					log.Printf("checker-tls: enum %s:%d → versions=%d duration=%dms",
+						pr.Host, pr.Port, len(enumRes.Versions), enumRes.DurationMS)
+				case skipReason != "":
+					log.Printf("checker-tls: enum %s:%d → skipped: %s",
+						pr.Host, pr.Port, skipReason)
+				}
+			}
 			mu.Lock()
 			probes[e.Ref] = pr
 			mu.Unlock()
diff --git a/checker/definition.go b/checker/definition.go
index b948e5b..4fd166a 100644
--- a/checker/definition.go
+++ b/checker/definition.go
@@ -29,6 +29,13 @@ func (p *tlsProvider) Definition() *sdk.CheckerDefinition {
 					Description: "Maximum time allowed for dial + STARTTLS + TLS handshake on a single endpoint.",
 					Default:     float64(DefaultProbeTimeoutMs),
 				},
+				{
+					Id:          OptionEnumerateCiphers,
+					Type:        "boolean",
+					Label:       "Enumerate accepted TLS versions and cipher suites",
+					Description: "When enabled, each direct-TLS endpoint is swept with one ClientHello per (version, cipher) pair to discover the exact set the server accepts. Adds ~50 handshakes per endpoint.",
+					Default:     false,
+				},
 			},
 			RunOpts: []sdk.CheckerOptionDocumentation{
 				{
diff --git a/checker/enumerate.go b/checker/enumerate.go
new file mode 100644
index 0000000..61e76ef
--- /dev/null
+++ b/checker/enumerate.go
@@ -0,0 +1,68 @@
+package checker
+
+import (
+	"context"
+	"net"
+	"strconv"
+	"strings"
+	"time"
+
+	"git.happydns.org/checker-tls/contract"
+	"git.happydns.org/checker-tls/tlsenum"
+)
+
+// enumerationProbeTimeout caps each individual sub-probe. It is intentionally
+// shorter than the main probe timeout: a sweep does dozens of handshakes and
+// most rejections come back in tens of ms, so 3s is enough to absorb a slow
+// network without dragging the total cost.
+const enumerationProbeTimeout = 3 * time.Second
+
+// enumerateEndpoint runs a (version × cipher) sweep against an endpoint —
+// direct TLS or STARTTLS — and returns the result in the wire-format consumed
+// by rules. It returns (nil, "<reason>") to signal the sweep was deliberately
+// skipped.
+func enumerateEndpoint(ctx context.Context, ep contract.TLSEndpoint, totalBudget time.Duration) (*TLSEnumeration, string) {
+	host := strings.TrimSuffix(ep.Host, ".")
+	addr := net.JoinHostPort(host, strconv.Itoa(int(ep.Port)))
+	sni := ep.SNI
+	if sni == "" {
+		sni = host
+	}
+
+	upgrader, ok := upgraderFor(ep.STARTTLS, sni)
+	if !ok {
+		return nil, "unsupported starttls dialect: " + ep.STARTTLS
+	}
+
+	sweepCtx := ctx
+	if totalBudget > 0 {
+		var cancel context.CancelFunc
+		sweepCtx, cancel = context.WithTimeout(ctx, totalBudget)
+		defer cancel()
+	}
+
+	start := time.Now()
+	res, err := tlsenum.Enumerate(sweepCtx, addr, sni, tlsenum.EnumerateOptions{
+		ProbeTimeout: enumerationProbeTimeout,
+		Upgrader:     upgrader,
+	})
+	elapsed := time.Since(start).Milliseconds()
+	if err != nil {
+		return &TLSEnumeration{Skipped: "enumeration error: " + err.Error(), DurationMS: elapsed}, ""
+	}
+
+	out := &TLSEnumeration{DurationMS: elapsed}
+	for _, v := range res.SupportedVersions {
+		ev := EnumVersion{Version: v, Name: tlsenum.VersionName(v)}
+		for _, c := range res.CiphersByVersion[v] {
+			ev.Ciphers = append(ev.Ciphers, EnumCipher{ID: c.ID, Name: c.Name})
+		}
+		out.Versions = append(out.Versions, ev)
+	}
+	return out, ""
+}
+
+// enumerationBudget is the upper bound we give one endpoint's sweep. ~50
+// handshakes × enumerationProbeTimeout would be 2-3 minutes worst case; we
+// cap at 60s so a black-holing target can't stall the whole collect run.
+const enumerationBudget = 60 * time.Second
diff --git a/checker/enumerate_test.go b/checker/enumerate_test.go
new file mode 100644
index 0000000..02484bc
--- /dev/null
+++ b/checker/enumerate_test.go
@@ -0,0 +1,198 @@
+package checker
+
+import (
+	"context"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/tls"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/pem"
+	"io"
+	"math/big"
+	"net"
+	"strconv"
+	"testing"
+	"time"
+
+	"git.happydns.org/checker-tls/contract"
+)
+
+// startEnumTestServer spins up a TCP listener that, for every accepted
+// connection: (1) optionally drives a fake STARTTLS dialect handshake, then
+// (2) lets the standard library terminate TLS with the provided cert. It
+// keeps accepting until the test closes the listener.
+//
+// We use the stdlib tls.Server (not utls) on the server side: the point of
+// these tests is to exercise the *checker* glue (upgraderFor + enumerate)
+// against the real client-side code, not to replay tlsenum's internals.
+func startEnumTestServer(t *testing.T, withSTARTTLS bool, cert tls.Certificate) net.Listener {
+	t.Helper()
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("listen: %v", err)
+	}
+	go func() {
+		for {
+			c, err := ln.Accept()
+			if err != nil {
+				return
+			}
+			go handleEnumConn(c, withSTARTTLS, cert)
+		}
+	}()
+	return ln
+}
+
+func handleEnumConn(c net.Conn, withSTARTTLS bool, cert tls.Certificate) {
+	defer c.Close()
+	if withSTARTTLS {
+		// Pretend to be SMTP: 220 banner, EHLO ack, STARTTLS ack. The
+		// implementation of starttlsSMTP only requires the server to
+		// advertise STARTTLS in its EHLO response and to reply with a 2xx
+		// to the STARTTLS verb — exact verbs come from RFC 3207.
+		if _, err := io.WriteString(c, "220 enum.test ESMTP\r\n"); err != nil {
+			return
+		}
+		buf := make([]byte, 1024)
+		// EHLO line
+		if _, err := c.Read(buf); err != nil {
+			return
+		}
+		if _, err := io.WriteString(c, "250-enum.test\r\n250 STARTTLS\r\n"); err != nil {
+			return
+		}
+		// STARTTLS line
+		if _, err := c.Read(buf); err != nil {
+			return
+		}
+		if _, err := io.WriteString(c, "220 ready\r\n"); err != nil {
+			return
+		}
+	}
+	tc := tls.Server(c, &tls.Config{
+		Certificates: []tls.Certificate{cert},
+		MinVersion:   tls.VersionTLS12,
+		MaxVersion:   tls.VersionTLS12, // narrow surface so the sweep is fast
+	})
+	defer tc.Close()
+	_ = tc.Handshake()
+}
+
+// enumTestCert is a one-time self-signed ECDSA cert reused across tests.
+func enumTestCert(t *testing.T) tls.Certificate {
+	t.Helper()
+	key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	if err != nil {
+		t.Fatalf("genkey: %v", err)
+	}
+	tmpl := x509.Certificate{
+		SerialNumber: big.NewInt(1),
+		Subject:      pkix.Name{CommonName: "enum.test"},
+		NotBefore:    time.Now().Add(-time.Hour),
+		NotAfter:     time.Now().Add(time.Hour),
+		DNSNames:     []string{"enum.test"},
+		KeyUsage:     x509.KeyUsageDigitalSignature,
+		ExtKeyUsage:  []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
+	}
+	der, err := x509.CreateCertificate(rand.Reader, &tmpl, &tmpl, &key.PublicKey, key)
+	if err != nil {
+		t.Fatalf("createcert: %v", err)
+	}
+	keyDER, err := x509.MarshalECPrivateKey(key)
+	if err != nil {
+		t.Fatalf("marshal key: %v", err)
+	}
+	c, err := tls.X509KeyPair(
+		pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: der}),
+		pem.EncodeToMemory(&pem.Block{Type: "EC PRIVATE KEY", Bytes: keyDER}),
+	)
+	if err != nil {
+		t.Fatalf("keypair: %v", err)
+	}
+	return c
+}
+
+func portOf(t *testing.T, ln net.Listener) uint16 {
+	t.Helper()
+	_, p, err := net.SplitHostPort(ln.Addr().String())
+	if err != nil {
+		t.Fatalf("split addr: %v", err)
+	}
+	n, err := strconv.ParseUint(p, 10, 16)
+	if err != nil {
+		t.Fatalf("parse port: %v", err)
+	}
+	return uint16(n)
+}
+
+// TestEnumerateEndpoint_DirectTLS asserts the sweep returns at least one
+// supported version + cipher when the endpoint is plain TLS — proving the
+// nil-upgrader path of upgraderFor wires correctly.
+func TestEnumerateEndpoint_DirectTLS(t *testing.T) {
+	cert := enumTestCert(t)
+	ln := startEnumTestServer(t, false, cert)
+	defer ln.Close()
+
+	res, skip := enumerateEndpoint(context.Background(), contract.TLSEndpoint{
+		Host: "127.0.0.1",
+		Port: portOf(t, ln),
+		SNI:  "enum.test",
+	}, 30*time.Second)
+	if skip != "" {
+		t.Fatalf("unexpected skip reason: %q", skip)
+	}
+	if res == nil || len(res.Versions) == 0 {
+		t.Fatalf("expected at least one supported version, got %+v", res)
+	}
+	gotTLS12 := false
+	for _, v := range res.Versions {
+		if v.Version == tls.VersionTLS12 && len(v.Ciphers) > 0 {
+			gotTLS12 = true
+		}
+	}
+	if !gotTLS12 {
+		t.Fatalf("expected TLS 1.2 with at least one cipher, got %+v", res.Versions)
+	}
+}
+
+// TestEnumerateEndpoint_SMTP_STARTTLS asserts the sweep drives the SMTP
+// dialect upgrade on every sub-probe and still discovers ciphers — proving
+// the upgraderFor("smtp", sni) path is wired into Enumerate.
+func TestEnumerateEndpoint_SMTP_STARTTLS(t *testing.T) {
+	cert := enumTestCert(t)
+	ln := startEnumTestServer(t, true, cert)
+	defer ln.Close()
+
+	res, skip := enumerateEndpoint(context.Background(), contract.TLSEndpoint{
+		Host:     "127.0.0.1",
+		Port:     portOf(t, ln),
+		SNI:      "enum.test",
+		STARTTLS: "smtp",
+	}, 60*time.Second)
+	if skip != "" {
+		t.Fatalf("unexpected skip reason: %q", skip)
+	}
+	if res == nil || len(res.Versions) == 0 {
+		t.Fatalf("expected at least one supported version through STARTTLS, got %+v", res)
+	}
+}
+
+// TestEnumerateEndpoint_UnknownDialect asserts an unsupported STARTTLS
+// dialect is rejected with a non-empty skip reason and no result — the
+// observation must record *why* enumeration didn't run, not silently report
+// "no versions accepted".
+func TestEnumerateEndpoint_UnknownDialect(t *testing.T) {
+	res, skip := enumerateEndpoint(context.Background(), contract.TLSEndpoint{
+		Host:     "127.0.0.1",
+		Port:     1, // unreachable on purpose; we never get past the dialect check
+		STARTTLS: "no-such-dialect",
+	}, time.Second)
+	if res != nil {
+		t.Fatalf("expected nil result for unknown dialect, got %+v", res)
+	}
+	if skip == "" {
+		t.Fatalf("expected non-empty skip reason for unknown dialect")
+	}
+}
diff --git a/checker/rule.go b/checker/rule.go
index bcb1858..ad9d626 100644
--- a/checker/rule.go
+++ b/checker/rule.go
@@ -25,6 +25,8 @@ func Rules() []sdk.CheckRule {
 		&expiryRule{},
 		&tlsVersionRule{},
 		&cipherSuiteRule{},
+		&versionEnumerationRule{},
+		&weakCipherRule{},
 	}
 }
 
diff --git a/checker/rules_enumeration.go b/checker/rules_enumeration.go
new file mode 100644
index 0000000..6757be0
--- /dev/null
+++ b/checker/rules_enumeration.go
@@ -0,0 +1,197 @@
+package checker
+
+import (
+	"context"
+	"crypto/tls"
+	"fmt"
+	"sort"
+	"strings"
+
+	sdk "git.happydns.org/checker-sdk-go/checker"
+)
+
+// hasEnum returns true when at least one probe carries enumeration data.
+// Rules use this to short-circuit to "skipped" when the user hasn't enabled
+// the enumerate option (rather than falsely emitting a "passing" verdict).
+func hasEnum(data *TLSData) bool {
+	for _, p := range data.Probes {
+		if p.Enum != nil && len(p.Enum.Versions) > 0 {
+			return true
+		}
+	}
+	return false
+}
+
+// versionEnumerationRule reports the full set of protocol versions accepted
+// by each endpoint, and flags any acceptance below the TLS 1.2 floor — the
+// regular handshake rule only sees the *negotiated* version, so a server
+// that still accepts TLS 1.0 alongside TLS 1.3 would otherwise look healthy.
+type versionEnumerationRule struct{}
+
+func (r *versionEnumerationRule) Name() string { return "tls.enum.versions" }
+func (r *versionEnumerationRule) Description() string {
+	return "Flags endpoints that still accept TLS versions below TLS 1.2 (requires the enumerate option)."
+}
+
+func (r *versionEnumerationRule) Evaluate(ctx context.Context, obs sdk.ObservationGetter, _ sdk.CheckerOptions) []sdk.CheckState {
+	data, errSt := loadData(ctx, obs)
+	if errSt != nil {
+		return []sdk.CheckState{*errSt}
+	}
+	if len(data.Probes) == 0 {
+		return []sdk.CheckState{emptyCaseState("tls.enum.versions.no_endpoints")}
+	}
+	if !hasEnum(data) {
+		return []sdk.CheckState{unknownState(
+			"tls.enum.versions.skipped",
+			"TLS version/cipher enumeration was not run for any endpoint (enable the enumerateCiphers option).",
+		)}
+	}
+
+	var out []sdk.CheckState
+	anyEnum := false
+	for _, ref := range sortedRefs(data) {
+		p := data.Probes[ref]
+		if p.Enum == nil || len(p.Enum.Versions) == 0 {
+			continue
+		}
+		anyEnum = true
+
+		var legacy []string
+		for _, v := range p.Enum.Versions {
+			if v.Version < tls.VersionTLS12 {
+				legacy = append(legacy, v.Name)
+			}
+		}
+		if len(legacy) == 0 {
+			continue
+		}
+		sort.Strings(legacy)
+		out = append(out, sdk.CheckState{
+			Status:  sdk.StatusWarn,
+			Code:    "tls.enum.versions.legacy_accepted",
+			Subject: subjectOf(p),
+			Message: fmt.Sprintf("Endpoint accepts legacy protocol version(s): %s.", strings.Join(legacy, ", ")),
+			Meta:    metaOf(p),
+		})
+	}
+	if !anyEnum {
+		return []sdk.CheckState{unknownState(
+			"tls.enum.versions.skipped",
+			"No endpoint produced enumeration data.",
+		)}
+	}
+	if len(out) == 0 {
+		return []sdk.CheckState{passState(
+			"tls.enum.versions.ok",
+			"No endpoint accepts a protocol version below TLS 1.2.",
+		)}
+	}
+	return out
+}
+
+// weakCipherRule flags endpoints that accept cipher suites widely considered
+// broken or insecure: NULL, anonymous, EXPORT, RC4, 3DES, and any other CBC
+// suite using SHA-1 in MAC-then-encrypt mode is *not* flagged here because
+// real-world servers still need them for legacy clients; this rule limits
+// itself to the set with no defensible use in 2026.
+type weakCipherRule struct{}
+
+func (r *weakCipherRule) Name() string { return "tls.enum.ciphers" }
+func (r *weakCipherRule) Description() string {
+	return "Flags endpoints that accept broken cipher suites (NULL, anonymous, EXPORT, RC4, 3DES)."
+}
+
+// classifyCipher returns a non-empty category when the named cipher belongs
+// to a class with no defensible modern use. The check is by substring on the
+// IANA name because every entry follows the TLS_<KX>_WITH_<CIPHER>_<MAC>
+// convention.
+func classifyCipher(name string) string {
+	upper := strings.ToUpper(name)
+	switch {
+	case strings.Contains(upper, "_NULL_"), strings.HasSuffix(upper, "_NULL"):
+		return "NULL"
+	case strings.Contains(upper, "_ANON_"):
+		return "anonymous"
+	case strings.Contains(upper, "_EXPORT_"):
+		return "EXPORT"
+	case strings.Contains(upper, "_RC4_"):
+		return "RC4"
+	case strings.Contains(upper, "_3DES_"), strings.Contains(upper, "_DES_"):
+		return "3DES/DES"
+	}
+	return ""
+}
+
+func (r *weakCipherRule) Evaluate(ctx context.Context, obs sdk.ObservationGetter, _ sdk.CheckerOptions) []sdk.CheckState {
+	data, errSt := loadData(ctx, obs)
+	if errSt != nil {
+		return []sdk.CheckState{*errSt}
+	}
+	if len(data.Probes) == 0 {
+		return []sdk.CheckState{emptyCaseState("tls.enum.ciphers.no_endpoints")}
+	}
+	if !hasEnum(data) {
+		return []sdk.CheckState{unknownState(
+			"tls.enum.ciphers.skipped",
+			"TLS version/cipher enumeration was not run for any endpoint (enable the enumerateCiphers option).",
+		)}
+	}
+
+	var out []sdk.CheckState
+	anyEnum := false
+	for _, ref := range sortedRefs(data) {
+		p := data.Probes[ref]
+		if p.Enum == nil || len(p.Enum.Versions) == 0 {
+			continue
+		}
+		anyEnum = true
+
+		// Aggregate by category so a server accepting six EXPORT suites
+		// produces one finding, not six.
+		byCategory := map[string][]string{}
+		for _, v := range p.Enum.Versions {
+			for _, c := range v.Ciphers {
+				cat := classifyCipher(c.Name)
+				if cat == "" {
+					continue
+				}
+				byCategory[cat] = append(byCategory[cat], c.Name)
+			}
+		}
+		if len(byCategory) == 0 {
+			continue
+		}
+		cats := make([]string, 0, len(byCategory))
+		for c := range byCategory {
+			cats = append(cats, c)
+		}
+		sort.Strings(cats)
+		parts := make([]string, 0, len(cats))
+		for _, c := range cats {
+			parts = append(parts, fmt.Sprintf("%s (%d)", c, len(byCategory[c])))
+		}
+		meta := metaOf(p)
+		meta["weak_ciphers"] = byCategory
+		out = append(out, sdk.CheckState{
+			Status:  sdk.StatusWarn,
+			Code:    "tls.enum.ciphers.weak_accepted",
+			Subject: subjectOf(p),
+			Message: "Endpoint accepts broken cipher suites: " + strings.Join(parts, ", ") + ".",
+			Meta:    meta,
+		})
+	}
+	if !anyEnum {
+		return []sdk.CheckState{unknownState(
+			"tls.enum.ciphers.skipped",
+			"No endpoint produced enumeration data.",
+		)}
+	}
+	if len(out) == 0 {
+		return []sdk.CheckState{passState(
+			"tls.enum.ciphers.ok",
+			"No endpoint accepts a known-broken cipher suite (NULL/anonymous/EXPORT/RC4/3DES).",
+		)}
+	}
+	return out
+}
diff --git a/checker/rules_enumeration_test.go b/checker/rules_enumeration_test.go
new file mode 100644
index 0000000..3097477
--- /dev/null
+++ b/checker/rules_enumeration_test.go
@@ -0,0 +1,135 @@
+package checker
+
+import (
+	"context"
+	"crypto/tls"
+	"encoding/json"
+	"strings"
+	"testing"
+	"time"
+
+	sdk "git.happydns.org/checker-sdk-go/checker"
+)
+
+// stubObs is a minimal ObservationGetter that serves a pre-built TLSData
+// payload and ignores related lookups. It is local to this file rather than
+// promoted to a shared helper to keep the rule tests self-contained.
+type stubObs struct{ data TLSData }
+
+func (s stubObs) Get(_ context.Context, key sdk.ObservationKey, dest any) error {
+	if key != ObservationKeyTLSProbes {
+		return nil
+	}
+	raw, _ := json.Marshal(s.data)
+	return json.Unmarshal(raw, dest)
+}
+func (s stubObs) GetRelated(_ context.Context, _ sdk.ObservationKey) ([]sdk.RelatedObservation, error) {
+	return nil, nil
+}
+
+func newProbeWithEnum(versions ...EnumVersion) TLSProbe {
+	return TLSProbe{
+		Host: "example.test", Port: 443, Endpoint: "example.test:443", Type: "tls",
+		TLSHandshakeOK: true, TLSVersionNum: tls.VersionTLS13,
+		Enum: &TLSEnumeration{Versions: versions},
+	}
+}
+
+func TestVersionEnumerationRule_Skipped_NoEnum(t *testing.T) {
+	obs := stubObs{data: TLSData{
+		Probes:      map[string]TLSProbe{"a": {Host: "x", Port: 443, Endpoint: "x:443", Type: "tls", TLSHandshakeOK: true}},
+		CollectedAt: time.Now(),
+	}}
+	got := (&versionEnumerationRule{}).Evaluate(context.Background(), obs, nil)
+	if len(got) != 1 || got[0].Code != "tls.enum.versions.skipped" {
+		t.Fatalf("want a single skipped state, got %+v", got)
+	}
+}
+
+func TestVersionEnumerationRule_OK_OnlyModern(t *testing.T) {
+	obs := stubObs{data: TLSData{
+		Probes: map[string]TLSProbe{
+			"a": newProbeWithEnum(
+				EnumVersion{Version: tls.VersionTLS12, Name: "TLS 1.2"},
+				EnumVersion{Version: tls.VersionTLS13, Name: "TLS 1.3"},
+			),
+		},
+	}}
+	got := (&versionEnumerationRule{}).Evaluate(context.Background(), obs, nil)
+	if len(got) != 1 || got[0].Status != sdk.StatusOK || got[0].Code != "tls.enum.versions.ok" {
+		t.Fatalf("want a single OK state, got %+v", got)
+	}
+}
+
+func TestVersionEnumerationRule_LegacyAccepted(t *testing.T) {
+	obs := stubObs{data: TLSData{
+		Probes: map[string]TLSProbe{
+			"a": newProbeWithEnum(
+				EnumVersion{Version: tls.VersionTLS10, Name: "TLS 1.0"},
+				EnumVersion{Version: tls.VersionTLS12, Name: "TLS 1.2"},
+			),
+		},
+	}}
+	got := (&versionEnumerationRule{}).Evaluate(context.Background(), obs, nil)
+	if len(got) != 1 || got[0].Status != sdk.StatusWarn || got[0].Code != "tls.enum.versions.legacy_accepted" {
+		t.Fatalf("want a single warn state, got %+v", got)
+	}
+	if !strings.Contains(got[0].Message, "TLS 1.0") {
+		t.Fatalf("warn message should mention the legacy version, got %q", got[0].Message)
+	}
+}
+
+func TestClassifyCipher(t *testing.T) {
+	cases := map[string]string{
+		"TLS_RSA_WITH_NULL_SHA":                       "NULL",
+		"TLS_DH_anon_WITH_AES_128_CBC_SHA":            "anonymous",
+		"TLS_RSA_EXPORT_WITH_RC4_40_MD5":              "EXPORT",
+		"TLS_ECDHE_RSA_WITH_RC4_128_SHA":              "RC4",
+		"TLS_RSA_WITH_3DES_EDE_CBC_SHA":               "3DES/DES",
+		"TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256":       "",
+		"TLS_AES_256_GCM_SHA384":                      "",
+		"TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256": "",
+	}
+	for name, want := range cases {
+		if got := classifyCipher(name); got != want {
+			t.Errorf("classifyCipher(%q) = %q, want %q", name, got, want)
+		}
+	}
+}
+
+func TestWeakCipherRule_Detects(t *testing.T) {
+	obs := stubObs{data: TLSData{
+		Probes: map[string]TLSProbe{
+			"a": newProbeWithEnum(
+				EnumVersion{Version: tls.VersionTLS12, Name: "TLS 1.2", Ciphers: []EnumCipher{
+					{ID: 0xC02F, Name: "TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256"},
+					{ID: 0x000A, Name: "TLS_RSA_WITH_3DES_EDE_CBC_SHA"},
+					{ID: 0x0005, Name: "TLS_RSA_WITH_RC4_128_SHA"},
+				}},
+			),
+		},
+	}}
+	got := (&weakCipherRule{}).Evaluate(context.Background(), obs, nil)
+	if len(got) != 1 || got[0].Status != sdk.StatusWarn || got[0].Code != "tls.enum.ciphers.weak_accepted" {
+		t.Fatalf("want a single weak warn state, got %+v", got)
+	}
+	if !strings.Contains(got[0].Message, "RC4") || !strings.Contains(got[0].Message, "3DES/DES") {
+		t.Fatalf("warn message should list the broken categories, got %q", got[0].Message)
+	}
+}
+
+func TestWeakCipherRule_OK_OnlyModern(t *testing.T) {
+	obs := stubObs{data: TLSData{
+		Probes: map[string]TLSProbe{
+			"a": newProbeWithEnum(
+				EnumVersion{Version: tls.VersionTLS13, Name: "TLS 1.3", Ciphers: []EnumCipher{
+					{ID: 0x1301, Name: "TLS_AES_128_GCM_SHA256"},
+				}},
+			),
+		},
+	}}
+	got := (&weakCipherRule{}).Evaluate(context.Background(), obs, nil)
+	if len(got) != 1 || got[0].Status != sdk.StatusOK || got[0].Code != "tls.enum.ciphers.ok" {
+		t.Fatalf("want a single OK state, got %+v", got)
+	}
+}
diff --git a/checker/starttls.go b/checker/starttls.go
index 892e533..b06adf6 100644
--- a/checker/starttls.go
+++ b/checker/starttls.go
@@ -48,3 +48,18 @@ var starttlsUpgraders = map[string]starttlsUpgrader{}
 func registerStartTLS(protocol string, upgrader starttlsUpgrader) {
 	starttlsUpgraders[protocol] = upgrader
 }
+
+// upgraderFor returns a tlsenum-compatible upgrader callback for a given
+// STARTTLS dialect, plus an ok flag. An empty dialect means direct TLS and
+// returns (nil, true) — tlsenum will skip the upgrade phase. An unknown
+// dialect returns (nil, false) so the caller can record the skip reason.
+func upgraderFor(dialect, sni string) (func(net.Conn) error, bool) {
+	if dialect == "" {
+		return nil, true
+	}
+	up, ok := starttlsUpgraders[dialect]
+	if !ok {
+		return nil, false
+	}
+	return func(c net.Conn) error { return up(c, sni) }, true
+}
diff --git a/checker/starttls_ldap.go b/checker/starttls_ldap.go
index 30b47d3..40d1c5d 100644
--- a/checker/starttls_ldap.go
+++ b/checker/starttls_ldap.go
@@ -52,7 +52,10 @@ func starttlsLDAP(conn net.Conn, sni string) error {
 	if err != nil {
 		return fmt.Errorf("read response length: %w", err)
 	}
-	if length <= 0 || length > 4096 {
+	// 16 KiB comfortably accommodates an ExtendedResponse with a verbose
+	// diagnosticMessage while still bounding memory against a hostile peer.
+	const maxLDAPResponseBytes = 16 * 1024
+	if length <= 0 || length > maxLDAPResponseBytes {
 		return fmt.Errorf("unreasonable LDAP response length %d", length)
 	}
 	body := make([]byte, length)
diff --git a/checker/starttls_test.go b/checker/starttls_test.go
index 9d05e8f..0f76ebd 100644
--- a/checker/starttls_test.go
+++ b/checker/starttls_test.go
@@ -132,6 +132,24 @@ func TestStartTLS_IMAP_OK(t *testing.T) {
 	}
 }
 
+func TestStartTLS_IMAP_Refused(t *testing.T) {
+	err := runStartTLS(t, starttlsIMAP, "imap.example.com", func(c net.Conn) error {
+		br := bufio.NewReader(c)
+		_, _ = io.WriteString(c, "* OK IMAP4rev1 ready\r\n")
+		_, _ = readLineCRLF(br)
+		_, _ = io.WriteString(c, "* CAPABILITY IMAP4rev1 STARTTLS\r\nA001 OK CAPABILITY completed\r\n")
+		_, _ = readLineCRLF(br)
+		_, err := io.WriteString(c, "A002 NO STARTTLS unavailable\r\n")
+		return err
+	})
+	if err == nil {
+		t.Fatal("expected refusal error")
+	}
+	if errors.Is(err, errStartTLSNotOffered) {
+		t.Fatalf("refusal should not be classified as not-offered: %v", err)
+	}
+}
+
 func TestStartTLS_IMAP_NotAdvertised(t *testing.T) {
 	err := runStartTLS(t, starttlsIMAP, "imap.example.com", func(c net.Conn) error {
 		br := bufio.NewReader(c)
@@ -185,6 +203,24 @@ func TestStartTLS_POP3_NotAdvertised(t *testing.T) {
 	}
 }
 
+func TestStartTLS_POP3_Refused(t *testing.T) {
+	err := runStartTLS(t, starttlsPOP3, "pop.example.com", func(c net.Conn) error {
+		br := bufio.NewReader(c)
+		_, _ = io.WriteString(c, "+OK POP3 ready\r\n")
+		_, _ = readLineCRLF(br)
+		_, _ = io.WriteString(c, "+OK capa list\r\nUSER\r\nSTLS\r\n.\r\n")
+		_, _ = readLineCRLF(br)
+		_, err := io.WriteString(c, "-ERR STLS unavailable\r\n")
+		return err
+	})
+	if err == nil {
+		t.Fatal("expected refusal error")
+	}
+	if errors.Is(err, errStartTLSNotOffered) {
+		t.Fatalf("refusal should not be classified as not-offered: %v", err)
+	}
+}
+
 func TestStartTLS_XMPP_OK(t *testing.T) {
 	err := runStartTLS(t, starttlsXMPPClient, "xmpp.example.com", func(c net.Conn) error {
 		br := bufio.NewReader(c)
@@ -225,6 +261,47 @@ func TestStartTLS_XMPP_NotAdvertised(t *testing.T) {
 	}
 }
 
+func TestStartTLS_XMPP_Refused(t *testing.T) {
+	err := runStartTLS(t, starttlsXMPPClient, "xmpp.example.com", func(c net.Conn) error {
+		br := bufio.NewReader(c)
+		buf := make([]byte, 1024)
+		if _, err := br.Read(buf); err != nil {
+			return err
+		}
+		_, _ = io.WriteString(c,
+			`<?xml version='1.0'?><stream:stream xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams' id='1' from='xmpp.example.com' version='1.0'>`+
+				`<stream:features><starttls xmlns='urn:ietf:params:xml:ns:xmpp-tls'/></stream:features>`)
+		if _, err := br.Read(buf); err != nil {
+			return err
+		}
+		_, err := io.WriteString(c, `<failure xmlns='urn:ietf:params:xml:ns:xmpp-tls'/>`)
+		return err
+	})
+	if err == nil {
+		t.Fatal("expected failure error")
+	}
+	if errors.Is(err, errStartTLSNotOffered) {
+		t.Fatalf("<failure/> should not be classified as not-offered: %v", err)
+	}
+}
+
+func TestStartTLS_XMPP_StreamError(t *testing.T) {
+	err := runStartTLS(t, starttlsXMPPClient, "xmpp.example.com", func(c net.Conn) error {
+		br := bufio.NewReader(c)
+		buf := make([]byte, 1024)
+		if _, err := br.Read(buf); err != nil {
+			return err
+		}
+		_, err := io.WriteString(c,
+			`<?xml version='1.0'?><stream:stream xmlns='jabber:client' xmlns:stream='http://etherx.jabber.org/streams' id='1' from='xmpp.example.com' version='1.0'>`+
+				`<stream:error><host-unknown xmlns='urn:ietf:params:xml:ns:xmpp-streams'/></stream:error>`)
+		return err
+	})
+	if err == nil {
+		t.Fatal("expected stream:error to surface as error")
+	}
+}
+
 func TestStartTLS_LDAP_OK(t *testing.T) {
 	err := runStartTLS(t, starttlsLDAP, "ldap.example.com", func(c net.Conn) error {
 		// Drain the StartTLS request (fixed 31 bytes: 0x30 0x1d + 29 bytes).
@@ -250,6 +327,86 @@ func TestStartTLS_LDAP_OK(t *testing.T) {
 	}
 }
 
+func TestStartTLS_LDAP_WrongTag(t *testing.T) {
+	err := runStartTLS(t, starttlsLDAP, "ldap.example.com", func(c net.Conn) error {
+		req := make([]byte, 31)
+		if _, err := io.ReadFull(c, req); err != nil {
+			return err
+		}
+		_, err := c.Write([]byte{0x42, 0x00})
+		return err
+	})
+	if err == nil {
+		t.Fatal("expected error for wrong tag")
+	}
+	if errors.Is(err, errStartTLSNotOffered) {
+		t.Fatalf("malformed response should not be classified as not-offered: %v", err)
+	}
+}
+
+func TestStartTLS_LDAP_OversizedLength(t *testing.T) {
+	err := runStartTLS(t, starttlsLDAP, "ldap.example.com", func(c net.Conn) error {
+		req := make([]byte, 31)
+		if _, err := io.ReadFull(c, req); err != nil {
+			return err
+		}
+		// SEQUENCE with long-form length = 0x10000 (64 KiB) — beyond our 16 KiB cap.
+		_, err := c.Write([]byte{0x30, 0x83, 0x01, 0x00, 0x00})
+		return err
+	})
+	if err == nil {
+		t.Fatal("expected oversized-length error")
+	}
+}
+
+func TestStartTLS_LDAP_TruncatedBody(t *testing.T) {
+	err := runStartTLS(t, starttlsLDAP, "ldap.example.com", func(c net.Conn) error {
+		req := make([]byte, 31)
+		if _, err := io.ReadFull(c, req); err != nil {
+			return err
+		}
+		// Announce 12 bytes of body, only send 5 then close.
+		_, err := c.Write([]byte{0x30, 0x0c, 0x02, 0x01, 0x01, 0x78, 0x07})
+		return err
+	})
+	if err == nil {
+		t.Fatal("expected error on truncated body")
+	}
+}
+
+func TestStartTLS_LDAP_DiagnosticMessageOver4KiB(t *testing.T) {
+	// A real-world response with a verbose diagnosticMessage can exceed the
+	// previous 4 KiB cap. Confirm the bumped 16 KiB cap accepts it.
+	const diagLen = 8000
+	diag := make([]byte, diagLen)
+	for i := range diag {
+		diag[i] = 'x'
+	}
+	err := runStartTLS(t, starttlsLDAP, "ldap.example.com", func(c net.Conn) error {
+		req := make([]byte, 31)
+		if _, err := io.ReadFull(c, req); err != nil {
+			return err
+		}
+		// Body: messageID(3) + extResp tag(1) + extResp len(3) + resultCode(3) + matchedDN(2) + diag tag+long-len(4) + diag bytes
+		// extResp inner length = resultCode(3) + matchedDN(2) + diagTLV(4+diagLen) = 9 + diagLen
+		extInner := 9 + diagLen
+		// Outer SEQUENCE inner length = messageID(3) + extResp TLV(1+3+extInner)
+		outerInner := 3 + 4 + extInner
+		buf := []byte{0x30, 0x82, byte(outerInner >> 8), byte(outerInner & 0xff)}
+		buf = append(buf, 0x02, 0x01, 0x01) // messageID
+		buf = append(buf, 0x78, 0x82, byte(extInner>>8), byte(extInner&0xff))
+		buf = append(buf, 0x0a, 0x01, 0x00) // resultCode = success
+		buf = append(buf, 0x04, 0x00)       // matchedDN ""
+		buf = append(buf, 0x04, 0x82, byte(diagLen>>8), byte(diagLen&0xff))
+		buf = append(buf, diag...)
+		_, err := c.Write(buf)
+		return err
+	})
+	if err != nil {
+		t.Fatalf("expected success with verbose diagnosticMessage, got: %v", err)
+	}
+}
+
 func TestStartTLS_LDAP_Refused(t *testing.T) {
 	err := runStartTLS(t, starttlsLDAP, "ldap.example.com", func(c net.Conn) error {
 		req := make([]byte, 31)
diff --git a/checker/starttls_xmpp.go b/checker/starttls_xmpp.go
index 22b421a..7b6e1ad 100644
--- a/checker/starttls_xmpp.go
+++ b/checker/starttls_xmpp.go
@@ -22,13 +22,20 @@ func starttlsXMPPServer(conn net.Conn, sni string) error {
 	return starttlsXMPP(conn, sni, "jabber:server")
 }
 
+// xmppPreTLSReadLimit caps the bytes the XML decoder may pull from an
+// untrusted peer before the TLS handshake. The legitimate pre-TLS exchange
+// (<stream:stream> opening + <stream:features> + <proceed/>) is well under
+// 1 KiB; 64 KiB is generous for non-malicious servers while bounding memory
+// against a peer that streams unbounded XML to exhaust the prober.
+const xmppPreTLSReadLimit = 64 * 1024
+
 func starttlsXMPP(conn net.Conn, sni, ns string) error {
 	header := fmt.Sprintf(`<?xml version='1.0'?><stream:stream xmlns='%s' xmlns:stream='http://etherx.jabber.org/streams' version='1.0' to='%s'>`, ns, sni)
 	if _, err := io.WriteString(conn, header); err != nil {
 		return fmt.Errorf("write stream header: %w", err)
 	}
 
-	dec := xml.NewDecoder(conn)
+	dec := xml.NewDecoder(&io.LimitedReader{R: conn, N: xmppPreTLSReadLimit})
 
 	// Read the inbound <stream:stream> opening and its <stream:features>.
 	// A peer that opens with <stream:error/> (or anything other than features)
diff --git a/checker/types.go b/checker/types.go
index 8cbf23d..a0d5389 100644
--- a/checker/types.go
+++ b/checker/types.go
@@ -9,8 +9,9 @@ const ObservationKeyTLSProbes = "tls_probes"
 
 // Option ids on CheckerOptions.
 const (
-	OptionEndpoints      = "endpoints"
-	OptionProbeTimeoutMs = "probeTimeoutMs"
+	OptionEndpoints        = "endpoints"
+	OptionProbeTimeoutMs   = "probeTimeoutMs"
+	OptionEnumerateCiphers = "enumerateCiphers"
 )
 
 // Defaults shared between the definition's Default field and the runtime
@@ -100,6 +101,12 @@ type TLSProbe struct {
 	Chain     []CertInfo `json:"chain,omitempty"`
 	ElapsedMS int64      `json:"elapsed_ms,omitempty"`
 
+	// Enum carries the protocol-version and cipher-suite sweep. It is only
+	// populated when the user enables OptionEnumerateCiphers. Direct TLS and
+	// supported STARTTLS dialects are both swept; a STARTTLS endpoint with
+	// an unknown dialect is skipped with a reason recorded in Enum.Skipped.
+	Enum *TLSEnumeration `json:"enum,omitempty"`
+
 	// Error is a compatibility summary of whichever raw error applies.
 	// Left for any external consumer still inspecting it; rules should
 	// look at TCPError / HandshakeError instead.
@@ -142,3 +149,31 @@ type CertInfo struct {
 const (
 	ExpiringSoonThreshold = 14 * 24 * time.Hour
 )
+
+// TLSEnumeration is the result of sweeping a (version × cipher) matrix
+// against an endpoint. The exact set the server accepts (rather than just the
+// one combination it negotiated under default Go preferences) lets rules flag
+// legacy versions and weak cipher suites that would otherwise stay invisible.
+type TLSEnumeration struct {
+	// Versions lists every protocol version for which at least one cipher
+	// was accepted, with the matching cipher suites.
+	Versions []EnumVersion `json:"versions,omitempty"`
+	// Skipped is set when enumeration was not attempted (e.g. STARTTLS
+	// endpoint, prior handshake failure). Empty when enumeration ran.
+	Skipped string `json:"skipped,omitempty"`
+	// DurationMS is the wall-clock time spent enumerating, for ops visibility.
+	DurationMS int64 `json:"duration_ms,omitempty"`
+}
+
+// EnumVersion is one accepted protocol version plus the ciphers it accepted.
+type EnumVersion struct {
+	Version uint16       `json:"version"`
+	Name    string       `json:"name"`
+	Ciphers []EnumCipher `json:"ciphers,omitempty"`
+}
+
+// EnumCipher is one accepted cipher suite.
+type EnumCipher struct {
+	ID   uint16 `json:"id"`
+	Name string `json:"name"`
+}
diff --git a/checker/upgrader_for_test.go b/checker/upgrader_for_test.go
new file mode 100644
index 0000000..3803649
--- /dev/null
+++ b/checker/upgrader_for_test.go
@@ -0,0 +1,91 @@
+package checker
+
+import (
+	"errors"
+	"net"
+	"testing"
+)
+
+// TestUpgraderFor_DirectTLS verifies that an empty dialect returns a nil
+// upgrader with ok=true: tlsenum's contract is that nil means "no upgrade
+// phase", so direct-TLS endpoints must round-trip through this branch
+// without producing a shim that would call into the registry.
+func TestUpgraderFor_DirectTLS(t *testing.T) {
+	up, ok := upgraderFor("", "example.test")
+	if !ok {
+		t.Fatalf("expected ok=true for empty dialect")
+	}
+	if up != nil {
+		t.Fatalf("expected nil upgrader for empty dialect, got %T", up)
+	}
+}
+
+func TestUpgraderFor_UnknownDialect(t *testing.T) {
+	up, ok := upgraderFor("totally-not-a-dialect", "example.test")
+	if ok {
+		t.Fatalf("expected ok=false for unknown dialect")
+	}
+	if up != nil {
+		t.Fatalf("expected nil upgrader for unknown dialect, got %T", up)
+	}
+}
+
+// TestUpgraderFor_KnownDialect_ForwardsSNI registers a temporary fake dialect
+// in the registry, asks upgraderFor for its callback, invokes the callback,
+// and asserts the registered upgrader received the expected SNI. We can't
+// reuse a real dialect for this because they all read/write protocol-specific
+// banners on the connection — the point of this test is the SNI plumbing in
+// the closure, not the dialect's own behavior.
+func TestUpgraderFor_KnownDialect_ForwardsSNI(t *testing.T) {
+	const dialect = "test-fake"
+	const wantSNI = "host.example.test"
+
+	var (
+		gotSNI  string
+		gotConn net.Conn
+	)
+	wantErr := errors.New("sentinel from fake upgrader")
+	registerStartTLS(dialect, func(c net.Conn, sni string) error {
+		gotConn = c
+		gotSNI = sni
+		return wantErr
+	})
+	defer delete(starttlsUpgraders, dialect)
+
+	up, ok := upgraderFor(dialect, wantSNI)
+	if !ok || up == nil {
+		t.Fatalf("expected non-nil upgrader and ok=true, got nil=%v ok=%v", up == nil, ok)
+	}
+
+	// Use a closed pipe end as a sentinel net.Conn — the registered upgrader
+	// captures it without doing I/O, so a real connection is unnecessary.
+	a, b := net.Pipe()
+	_ = a.Close()
+	_ = b.Close()
+
+	if err := up(a); !errors.Is(err, wantErr) {
+		t.Fatalf("expected sentinel error to propagate, got %v", err)
+	}
+	if gotSNI != wantSNI {
+		t.Fatalf("registered upgrader received SNI %q, want %q", gotSNI, wantSNI)
+	}
+	if gotConn != a {
+		t.Fatalf("registered upgrader received a different conn than the one passed in")
+	}
+}
+
+// TestUpgraderFor_RealDialects_AllRegistered guards against silently dropping
+// a dialect from the registry: every protocol referenced by the contract's
+// STARTTLS values must resolve to a non-nil upgrader. The list mirrors the
+// dialects implemented in starttls_*.go.
+func TestUpgraderFor_RealDialects_AllRegistered(t *testing.T) {
+	dialects := []string{"smtp", "submission", "imap", "pop3", "xmpp-client", "xmpp-server", "ldap"}
+	for _, d := range dialects {
+		t.Run(d, func(t *testing.T) {
+			up, ok := upgraderFor(d, "host.example")
+			if !ok || up == nil {
+				t.Fatalf("dialect %q is not registered", d)
+			}
+		})
+	}
+}
diff --git a/go.mod b/go.mod
index 9656a31..c23c67d 100644
--- a/go.mod
+++ b/go.mod
@@ -3,3 +3,11 @@ module git.happydns.org/checker-tls
 go 1.25.0
 
 require git.happydns.org/checker-sdk-go v1.5.0
+
+require (
+	github.com/andybalholm/brotli v1.0.6 // indirect
+	github.com/klauspost/compress v1.17.4 // indirect
+	github.com/refraction-networking/utls v1.8.2 // indirect
+	golang.org/x/crypto v0.36.0 // indirect
+	golang.org/x/sys v0.31.0 // indirect
+)
diff --git a/go.sum b/go.sum
index c389c68..c811775 100644
--- a/go.sum
+++ b/go.sum
@@ -1,2 +1,12 @@
 git.happydns.org/checker-sdk-go v1.5.0 h1:5uD5Cm6xJ+lwnhbJ09iCXGHbYS9zRh+Yh0NeBHkAPBY=
 git.happydns.org/checker-sdk-go v1.5.0/go.mod h1:aNAcfYFfbhvH9kJhE0Njp5GX0dQbxdRB0rJ0KvSC5nI=
+github.com/andybalholm/brotli v1.0.6 h1:Yf9fFpf49Zrxb9NlQaluyE92/+X7UVHlhMNJN2sxfOI=
+github.com/andybalholm/brotli v1.0.6/go.mod h1:fO7iG3H7G2nSZ7m0zPUDn85XEX2GTukHGRSepvi9Eig=
+github.com/klauspost/compress v1.17.4 h1:Ej5ixsIri7BrIjBkRZLTo6ghwrEtHFk7ijlczPW4fZ4=
+github.com/klauspost/compress v1.17.4/go.mod h1:/dCuZOvVtNoHsyb+cuJD3itjs3NbnF6KH9zAO4BDxPM=
+github.com/refraction-networking/utls v1.8.2 h1:j4Q1gJj0xngdeH+Ox/qND11aEfhpgoEvV+S9iJ2IdQo=
+github.com/refraction-networking/utls v1.8.2/go.mod h1:jkSOEkLqn+S/jtpEHPOsVv/4V4EVnelwbMQl4vCWXAM=
+golang.org/x/crypto v0.36.0 h1:AnAEvhDddvBdpY+uR+MyHmuZzzNqXSe/GvuDeob5L34=
+golang.org/x/crypto v0.36.0/go.mod h1:Y4J0ReaxCR1IMaabaSMugxJES1EpwhBHhv2bDHklZvc=
+golang.org/x/sys v0.31.0 h1:ioabZlmFYtWhL+TRYpcnNlLwhyxaM9kWTDEmfnprqik=
+golang.org/x/sys v0.31.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
diff --git a/tlsenum/ciphers.go b/tlsenum/ciphers.go
new file mode 100644
index 0000000..303bfdd
--- /dev/null
+++ b/tlsenum/ciphers.go
@@ -0,0 +1,103 @@
+package tlsenum
+
+// CipherSuite pairs an IANA TLS cipher suite ID with its standard name.
+//
+// The catalog below intentionally covers the "real-world" set: modern AEAD
+// suites used by TLS 1.2/1.3, plus a long tail of legacy CBC/RC4/3DES/EXPORT
+// suites we want to *detect* on remote servers (so we can flag them), even
+// though Go's stdlib refuses to negotiate them. utls lets us put any 16-bit
+// value in the offered list, so the server's accept/reject decision is the
+// source of truth.
+type CipherSuite struct {
+	ID   uint16
+	Name string
+	// TLS13 is true for the five TLS 1.3 AEAD suites; those must only be
+	// offered with TLS 1.3 ClientHellos.
+	TLS13 bool
+}
+
+// TLS13Ciphers are the AEAD suites defined for TLS 1.3 (RFC 8446 §B.4).
+var TLS13Ciphers = []CipherSuite{
+	{0x1301, "TLS_AES_128_GCM_SHA256", true},
+	{0x1302, "TLS_AES_256_GCM_SHA384", true},
+	{0x1303, "TLS_CHACHA20_POLY1305_SHA256", true},
+	{0x1304, "TLS_AES_128_CCM_SHA256", true},
+	{0x1305, "TLS_AES_128_CCM_8_SHA256", true},
+}
+
+// LegacyCiphers covers TLS 1.0/1.1/1.2 (and SSLv3) suites. Not exhaustive of
+// the IANA registry, but it includes everything any modern audit cares about:
+// ECDHE/DHE/RSA/PSK kex, AES-GCM/CCM/CBC, ChaCha20, 3DES, RC4, NULL, EXPORT,
+// anonymous, and a handful of GOST/CAMELLIA/ARIA entries seen in the wild.
+var LegacyCiphers = []CipherSuite{
+	// ECDHE-ECDSA
+	{0xC02B, "TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256", false},
+	{0xC02C, "TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384", false},
+	{0xCCA9, "TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256", false},
+	{0xC023, "TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA256", false},
+	{0xC024, "TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA384", false},
+	{0xC009, "TLS_ECDHE_ECDSA_WITH_AES_128_CBC_SHA", false},
+	{0xC00A, "TLS_ECDHE_ECDSA_WITH_AES_256_CBC_SHA", false},
+	{0xC008, "TLS_ECDHE_ECDSA_WITH_3DES_EDE_CBC_SHA", false},
+	{0xC007, "TLS_ECDHE_ECDSA_WITH_RC4_128_SHA", false},
+	{0xC006, "TLS_ECDHE_ECDSA_WITH_NULL_SHA", false},
+
+	// ECDHE-RSA
+	{0xC02F, "TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256", false},
+	{0xC030, "TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384", false},
+	{0xCCA8, "TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256", false},
+	{0xC027, "TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256", false},
+	{0xC028, "TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384", false},
+	{0xC013, "TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA", false},
+	{0xC014, "TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA", false},
+	{0xC012, "TLS_ECDHE_RSA_WITH_3DES_EDE_CBC_SHA", false},
+	{0xC011, "TLS_ECDHE_RSA_WITH_RC4_128_SHA", false},
+	{0xC010, "TLS_ECDHE_RSA_WITH_NULL_SHA", false},
+
+	// DHE-RSA
+	{0x009E, "TLS_DHE_RSA_WITH_AES_128_GCM_SHA256", false},
+	{0x009F, "TLS_DHE_RSA_WITH_AES_256_GCM_SHA384", false},
+	{0xCCAA, "TLS_DHE_RSA_WITH_CHACHA20_POLY1305_SHA256", false},
+	{0x0067, "TLS_DHE_RSA_WITH_AES_128_CBC_SHA256", false},
+	{0x006B, "TLS_DHE_RSA_WITH_AES_256_CBC_SHA256", false},
+	{0x0033, "TLS_DHE_RSA_WITH_AES_128_CBC_SHA", false},
+	{0x0039, "TLS_DHE_RSA_WITH_AES_256_CBC_SHA", false},
+	{0x0016, "TLS_DHE_RSA_WITH_3DES_EDE_CBC_SHA", false},
+
+	// Plain RSA
+	{0x009C, "TLS_RSA_WITH_AES_128_GCM_SHA256", false},
+	{0x009D, "TLS_RSA_WITH_AES_256_GCM_SHA384", false},
+	{0x003C, "TLS_RSA_WITH_AES_128_CBC_SHA256", false},
+	{0x003D, "TLS_RSA_WITH_AES_256_CBC_SHA256", false},
+	{0x002F, "TLS_RSA_WITH_AES_128_CBC_SHA", false},
+	{0x0035, "TLS_RSA_WITH_AES_256_CBC_SHA", false},
+	{0x000A, "TLS_RSA_WITH_3DES_EDE_CBC_SHA", false},
+	{0x0005, "TLS_RSA_WITH_RC4_128_SHA", false},
+	{0x0004, "TLS_RSA_WITH_RC4_128_MD5", false},
+	{0x003B, "TLS_RSA_WITH_NULL_SHA256", false},
+	{0x0002, "TLS_RSA_WITH_NULL_SHA", false},
+	{0x0001, "TLS_RSA_WITH_NULL_MD5", false},
+
+	// Anonymous (broken by design — flag if seen)
+	{0x006D, "TLS_DH_anon_WITH_AES_256_CBC_SHA256", false},
+	{0x0034, "TLS_DH_anon_WITH_AES_128_CBC_SHA", false},
+	{0x003A, "TLS_DH_anon_WITH_AES_256_CBC_SHA", false},
+	{0xC018, "TLS_ECDH_anon_WITH_AES_128_CBC_SHA", false},
+	{0xC019, "TLS_ECDH_anon_WITH_AES_256_CBC_SHA", false},
+
+	// EXPORT (40-bit, illegal since ~2000 — flag if seen)
+	{0x0008, "TLS_RSA_EXPORT_WITH_DES40_CBC_SHA", false},
+	{0x0014, "TLS_DHE_RSA_EXPORT_WITH_DES40_CBC_SHA", false},
+	{0x0017, "TLS_DH_anon_EXPORT_WITH_RC4_40_MD5", false},
+	{0x0019, "TLS_DH_anon_EXPORT_WITH_DES40_CBC_SHA", false},
+	{0x0003, "TLS_RSA_EXPORT_WITH_RC4_40_MD5", false},
+	{0x0006, "TLS_RSA_EXPORT_WITH_RC2_CBC_40_MD5", false},
+}
+
+// AllCiphers concatenates legacy and TLS 1.3 cipher suites.
+func AllCiphers() []CipherSuite {
+	out := make([]CipherSuite, 0, len(LegacyCiphers)+len(TLS13Ciphers))
+	out = append(out, LegacyCiphers...)
+	out = append(out, TLS13Ciphers...)
+	return out
+}
diff --git a/tlsenum/tlsenum.go b/tlsenum/tlsenum.go
new file mode 100644
index 0000000..b2a7562
--- /dev/null
+++ b/tlsenum/tlsenum.go
@@ -0,0 +1,283 @@
+// Package tlsenum probes a remote endpoint to discover the exact set of
+// SSL/TLS protocol versions and cipher suites it accepts.
+//
+// The Go stdlib's crypto/tls only negotiates a curated subset of modern
+// suites and refuses to even offer legacy ones (RC4, 3DES, EXPORT, NULL,
+// anonymous, …), so it cannot be used to *audit* what a server accepts.
+// Instead we use github.com/refraction-networking/utls to craft a fully
+// custom ClientHello carrying a single (version, cipher) pair and let the
+// server tell us — by ServerHello or alert — whether it accepts it.
+//
+// Scope of the minimal version:
+//   - TLS 1.0, 1.1, 1.2, 1.3 (negotiated via the SupportedVersions extension).
+//   - Direct TLS only; STARTTLS upgrade is the caller's responsibility for
+//     now (the existing checker package owns those dialect handlers).
+//   - SSLv3 and SSLv2 are deliberately out of scope; SSLv2 has a different
+//     wire format and would require either raw byte crafting or a legacy
+//     OpenSSL sidecar.
+package tlsenum
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"net"
+	"strconv"
+	"time"
+
+	utls "github.com/refraction-networking/utls"
+)
+
+// AllVersions is the set of protocol versions Probe knows how to offer.
+var AllVersions = []uint16{
+	utls.VersionTLS10,
+	utls.VersionTLS11,
+	utls.VersionTLS12,
+	utls.VersionTLS13,
+}
+
+// VersionName returns a human-readable label for a TLS protocol version.
+func VersionName(v uint16) string {
+	switch v {
+	case utls.VersionTLS10:
+		return "TLS 1.0"
+	case utls.VersionTLS11:
+		return "TLS 1.1"
+	case utls.VersionTLS12:
+		return "TLS 1.2"
+	case utls.VersionTLS13:
+		return "TLS 1.3"
+	default:
+		return "0x" + strconv.FormatUint(uint64(v), 16)
+	}
+}
+
+// ProbeResult is the outcome of a single (version, cipher) attempt.
+type ProbeResult struct {
+	OfferedVersion uint16
+	OfferedCipher  uint16
+
+	// Accepted is true when the server completed enough of the handshake to
+	// echo back a ServerHello with our offered version and cipher. We do not
+	// require a fully successful handshake (certificate verification can fail
+	// for unrelated reasons); ServerHello acceptance is what we measure.
+	Accepted bool
+
+	// NegotiatedVersion / NegotiatedCipher are populated when Accepted is
+	// true. They should match the offered values; if they differ, the server
+	// is misbehaving (or downgrading).
+	NegotiatedVersion uint16
+	NegotiatedCipher  uint16
+
+	// Err is the underlying error from the dial or handshake. For a clean
+	// "server rejected this combination" outcome it will typically be a TLS
+	// alert (handshake_failure, protocol_version, insufficient_security…).
+	Err error
+}
+
+// ProbeOptions controls a single Probe call.
+type ProbeOptions struct {
+	// Timeout bounds dial + (optional) upgrade + handshake. A zero value
+	// means no deadline beyond the parent context's.
+	Timeout time.Duration
+
+	// Upgrader, when non-nil, is invoked on the freshly-dialed connection
+	// before the TLS ClientHello is sent. It is the injection point for
+	// STARTTLS dialect handlers (SMTP, IMAP, POP3, …): the callback drives
+	// the plaintext exchange that requests the upgrade and returns nil once
+	// the connection is ready for tls.Client. tlsenum stays agnostic of the
+	// dialect; the caller owns that knowledge.
+	Upgrader func(net.Conn) error
+}
+
+// Probe attempts a TLS handshake against addr offering exactly one protocol
+// version and one cipher suite. It never panics; transport / handshake errors
+// are reported on the returned ProbeResult.
+//
+// addr must be host:port. sni is the SNI to send (pass the host if unsure).
+func Probe(ctx context.Context, addr, sni string, version, cipher uint16, opts ProbeOptions) ProbeResult {
+	res := ProbeResult{OfferedVersion: version, OfferedCipher: cipher}
+
+	dialCtx := ctx
+	if opts.Timeout > 0 {
+		var cancel context.CancelFunc
+		dialCtx, cancel = context.WithTimeout(ctx, opts.Timeout)
+		defer cancel()
+	}
+
+	d := &net.Dialer{}
+	raw, err := d.DialContext(dialCtx, "tcp", addr)
+	if err != nil {
+		res.Err = fmt.Errorf("dial: %w", err)
+		return res
+	}
+	defer raw.Close()
+	if dl, ok := dialCtx.Deadline(); ok {
+		_ = raw.SetDeadline(dl)
+	}
+
+	if opts.Upgrader != nil {
+		if err := opts.Upgrader(raw); err != nil {
+			res.Err = fmt.Errorf("upgrade: %w", err)
+			return res
+		}
+	}
+
+	cfg := &utls.Config{
+		ServerName:         sni,
+		InsecureSkipVerify: true, // #nosec G402 -- enumeration; we only care about handshake outcome
+	}
+	uc := utls.UClient(raw, cfg, utls.HelloCustom)
+	spec := buildSpec(version, cipher, sni)
+	if err := uc.ApplyPreset(&spec); err != nil {
+		res.Err = fmt.Errorf("apply-preset: %w", err)
+		return res
+	}
+
+	err = uc.Handshake()
+	state := uc.ConnectionState()
+	if err == nil {
+		res.Accepted = true
+		res.NegotiatedVersion = state.Version
+		res.NegotiatedCipher = state.CipherSuite
+		return res
+	}
+
+	// Some servers complete ServerHello (so we know they accepted version +
+	// cipher) but fail later — for example, certificate-mismatch or the
+	// client failing to verify. If state has a non-zero Version/CipherSuite
+	// matching what we offered, we still count it as accepted.
+	if state.Version == version && state.CipherSuite == cipher && state.CipherSuite != 0 {
+		res.Accepted = true
+		res.NegotiatedVersion = state.Version
+		res.NegotiatedCipher = state.CipherSuite
+	}
+	res.Err = err
+	return res
+}
+
+// EnumerateOptions controls Enumerate.
+type EnumerateOptions struct {
+	// Timeout for each individual probe. Defaults to 5s when zero.
+	ProbeTimeout time.Duration
+	// Versions to try. Defaults to AllVersions when nil.
+	Versions []uint16
+	// Ciphers to try. Defaults to AllCiphers() when nil. The TLS13 flag is
+	// honored: TLS 1.3 ciphers are only offered with TLS 1.3 probes, and
+	// vice-versa.
+	Ciphers []CipherSuite
+	// Upgrader, when non-nil, is forwarded to every sub-probe (see
+	// ProbeOptions.Upgrader). It is invoked on a freshly-dialed connection
+	// before each ClientHello, so STARTTLS dialect handlers run once per
+	// probe, not once for the whole sweep.
+	Upgrader func(net.Conn) error
+}
+
+// EnumerationResult is the aggregate outcome of an enumeration sweep.
+type EnumerationResult struct {
+	// SupportedVersions lists protocol versions for which at least one
+	// cipher was accepted.
+	SupportedVersions []uint16
+	// CiphersByVersion lists, per accepted version, the cipher suites the
+	// server agreed to negotiate.
+	CiphersByVersion map[uint16][]CipherSuite
+}
+
+// Enumerate sweeps a (version × cipher) matrix against addr and returns what
+// the server actually accepts. Probes are performed sequentially; concurrency
+// can be added later but tends to upset some middleboxes when probing too
+// hard.
+func Enumerate(ctx context.Context, addr, sni string, opts EnumerateOptions) (EnumerationResult, error) {
+	if opts.ProbeTimeout == 0 {
+		opts.ProbeTimeout = 5 * time.Second
+	}
+	versions := opts.Versions
+	if versions == nil {
+		versions = AllVersions
+	}
+	ciphers := opts.Ciphers
+	if ciphers == nil {
+		ciphers = AllCiphers()
+	}
+
+	out := EnumerationResult{
+		CiphersByVersion: make(map[uint16][]CipherSuite),
+	}
+	seenVersion := make(map[uint16]bool)
+
+	for _, v := range versions {
+		isTLS13 := v == utls.VersionTLS13
+		for _, c := range ciphers {
+			if c.TLS13 != isTLS13 {
+				continue
+			}
+			if err := ctx.Err(); err != nil {
+				return out, err
+			}
+			r := Probe(ctx, addr, sni, v, c.ID, ProbeOptions{
+				Timeout:  opts.ProbeTimeout,
+				Upgrader: opts.Upgrader,
+			})
+			if !r.Accepted {
+				continue
+			}
+			out.CiphersByVersion[v] = append(out.CiphersByVersion[v], c)
+			if !seenVersion[v] {
+				seenVersion[v] = true
+				out.SupportedVersions = append(out.SupportedVersions, v)
+			}
+		}
+	}
+	return out, nil
+}
+
+// buildSpec assembles a ClientHelloSpec offering exactly one cipher and one
+// protocol version. For TLS 1.3 the legacy version field stays at TLS 1.2 and
+// the real version is signalled through the SupportedVersions extension, per
+// RFC 8446 §4.1.2 / §4.2.1.
+func buildSpec(version, cipher uint16, sni string) utls.ClientHelloSpec {
+	tlsVersMin := version
+	tlsVersMax := version
+	if version == utls.VersionTLS13 {
+		// utls inspects TLSVersMax to decide whether to drive TLS 1.3
+		// machinery; the on-the-wire legacy_version stays TLS 1.2.
+		tlsVersMin = utls.VersionTLS12
+	}
+
+	exts := []utls.TLSExtension{
+		&utls.SNIExtension{ServerName: sni},
+		&utls.SupportedCurvesExtension{Curves: []utls.CurveID{
+			utls.X25519, utls.CurveP256, utls.CurveP384, utls.CurveP521,
+		}},
+		&utls.SupportedPointsExtension{SupportedPoints: []byte{0}}, // uncompressed
+		&utls.SignatureAlgorithmsExtension{SupportedSignatureAlgorithms: []utls.SignatureScheme{
+			utls.ECDSAWithP256AndSHA256, utls.ECDSAWithP384AndSHA384, utls.ECDSAWithP521AndSHA512,
+			utls.PSSWithSHA256, utls.PSSWithSHA384, utls.PSSWithSHA512,
+			utls.PKCS1WithSHA256, utls.PKCS1WithSHA384, utls.PKCS1WithSHA512,
+			utls.PKCS1WithSHA1, utls.ECDSAWithSHA1,
+		}},
+		&utls.RenegotiationInfoExtension{Renegotiation: utls.RenegotiateOnceAsClient},
+	}
+
+	if version == utls.VersionTLS13 {
+		exts = append(exts,
+			&utls.SupportedVersionsExtension{Versions: []uint16{utls.VersionTLS13}},
+			&utls.KeyShareExtension{KeyShares: []utls.KeyShare{
+				{Group: utls.X25519},
+			}},
+			&utls.PSKKeyExchangeModesExtension{Modes: []uint8{utls.PskModeDHE}},
+		)
+	}
+
+	return utls.ClientHelloSpec{
+		TLSVersMin:         tlsVersMin,
+		TLSVersMax:         tlsVersMax,
+		CipherSuites:       []uint16{cipher},
+		CompressionMethods: []byte{0}, // null
+		Extensions:         exts,
+	}
+}
+
+// ErrNoVersions is returned when an enumeration request asks for an empty set
+// of versions or ciphers.
+var ErrNoVersions = errors.New("tlsenum: no versions or ciphers to probe")
diff --git a/tlsenum/tlsenum_test.go b/tlsenum/tlsenum_test.go
new file mode 100644
index 0000000..7d94670
--- /dev/null
+++ b/tlsenum/tlsenum_test.go
@@ -0,0 +1,223 @@
+package tlsenum
+
+import (
+	"context"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	stdtls "crypto/tls"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/pem"
+	"errors"
+	"fmt"
+	"io"
+	"math/big"
+	"net"
+	"os"
+	"testing"
+	"time"
+
+	utls "github.com/refraction-networking/utls"
+)
+
+// selfSignedCert returns a brand-new in-memory self-signed cert + key for
+// "test.local", suitable for stdlib tls.Server.
+func selfSignedCert() (stdtls.Certificate, error) {
+	key, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
+	if err != nil {
+		return stdtls.Certificate{}, err
+	}
+	tmpl := x509.Certificate{
+		SerialNumber: big.NewInt(1),
+		Subject:      pkix.Name{CommonName: "test.local"},
+		NotBefore:    time.Now().Add(-time.Hour),
+		NotAfter:     time.Now().Add(time.Hour),
+		DNSNames:     []string{"test.local"},
+		KeyUsage:     x509.KeyUsageDigitalSignature,
+		ExtKeyUsage:  []x509.ExtKeyUsage{x509.ExtKeyUsageServerAuth},
+	}
+	der, err := x509.CreateCertificate(rand.Reader, &tmpl, &tmpl, &key.PublicKey, key)
+	if err != nil {
+		return stdtls.Certificate{}, err
+	}
+	keyDER, err := x509.MarshalECPrivateKey(key)
+	if err != nil {
+		return stdtls.Certificate{}, err
+	}
+	certPEM := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: der})
+	keyPEM := pem.EncodeToMemory(&pem.Block{Type: "EC PRIVATE KEY", Bytes: keyDER})
+	return stdtls.X509KeyPair(certPEM, keyPEM)
+}
+
+// runFakeStartTLSServer accepts one connection, expects a "STARTTLS\r\n"
+// line, replies "OK\r\n", then runs a TLS handshake. It returns once the
+// handshake completes (or fails) and the connection is closed.
+func runFakeStartTLSServer(ln net.Listener, cert stdtls.Certificate) error {
+	c, err := ln.Accept()
+	if err != nil {
+		return err
+	}
+	defer c.Close()
+	buf := make([]byte, len("STARTTLS\r\n"))
+	if _, err := io.ReadFull(c, buf); err != nil {
+		return err
+	}
+	if string(buf) != "STARTTLS\r\n" {
+		return fmt.Errorf("unexpected pre-tls line: %q", string(buf))
+	}
+	if _, err := c.Write([]byte("OK\r\n")); err != nil {
+		return err
+	}
+	tc := stdtls.Server(c, &stdtls.Config{
+		Certificates: []stdtls.Certificate{cert},
+		MinVersion:   stdtls.VersionTLS12,
+	})
+	defer tc.Close()
+	return tc.Handshake()
+}
+
+// liveTarget returns a host:port to enumerate against, or skips the test if
+// the environment hasn't opted in. Network tests are gated behind
+// TLSENUM_LIVE=1 so the unit-test suite stays hermetic.
+func liveTarget(t *testing.T) (addr, sni string) {
+	t.Helper()
+	if os.Getenv("TLSENUM_LIVE") == "" {
+		t.Skip("set TLSENUM_LIVE=1 to run live enumeration tests")
+	}
+	host := os.Getenv("TLSENUM_HOST")
+	if host == "" {
+		host = "tls-v1-2.badssl.com"
+	}
+	port := os.Getenv("TLSENUM_PORT")
+	if port == "" {
+		port = "1012"
+	}
+	return net.JoinHostPort(host, port), host
+}
+
+func TestProbe_TLS12_AESGCM(t *testing.T) {
+	addr, sni := liveTarget(t)
+	ctx, cancel := context.WithTimeout(context.Background(), 15*time.Second)
+	defer cancel()
+
+	r := Probe(ctx, addr, sni, utls.VersionTLS12, 0xC02F /* ECDHE-RSA-AES128-GCM-SHA256 */, ProbeOptions{Timeout: 5 * time.Second})
+	if !r.Accepted {
+		t.Fatalf("expected ECDHE-RSA-AES128-GCM-SHA256 to be accepted on TLS 1.2 target; got err=%v", r.Err)
+	}
+	if r.NegotiatedVersion != utls.VersionTLS12 {
+		t.Fatalf("negotiated version = %x, want %x", r.NegotiatedVersion, utls.VersionTLS12)
+	}
+}
+
+func TestEnumerate_BasicShape(t *testing.T) {
+	addr, sni := liveTarget(t)
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Minute)
+	defer cancel()
+
+	res, err := Enumerate(ctx, addr, sni, EnumerateOptions{
+		ProbeTimeout: 5 * time.Second,
+	})
+	if err != nil {
+		t.Fatalf("Enumerate: %v", err)
+	}
+	if len(res.SupportedVersions) == 0 {
+		t.Fatalf("no supported versions discovered")
+	}
+	for v, ciphers := range res.CiphersByVersion {
+		if len(ciphers) == 0 {
+			t.Errorf("version %s listed as supported but no ciphers recorded", VersionName(v))
+		}
+		t.Logf("%s: %d cipher(s)", VersionName(v), len(ciphers))
+	}
+}
+
+// TestProbe_UpgraderInvoked uses a tiny in-memory STARTTLS-style server: a
+// goroutine listens, reads one "STARTTLS\r\n" line, replies "OK\r\n", then
+// performs a real Go-stdlib TLS handshake. We probe through the matching
+// Upgrader and assert the handshake succeeds — proving the callback runs in
+// the right place between dial and ClientHello.
+func TestProbe_UpgraderInvoked(t *testing.T) {
+	cert, err := selfSignedCert()
+	if err != nil {
+		t.Fatalf("self-signed cert: %v", err)
+	}
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("listen: %v", err)
+	}
+	defer ln.Close()
+
+	srvDone := make(chan error, 1)
+	go func() { srvDone <- runFakeStartTLSServer(ln, cert) }()
+
+	upgrader := func(c net.Conn) error {
+		if _, err := c.Write([]byte("STARTTLS\r\n")); err != nil {
+			return err
+		}
+		buf := make([]byte, 16)
+		n, err := c.Read(buf)
+		if err != nil {
+			return err
+		}
+		if got := string(buf[:n]); got != "OK\r\n" {
+			return fmt.Errorf("unexpected reply: %q", got)
+		}
+		return nil
+	}
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+	r := Probe(ctx, ln.Addr().String(), "test.local",
+		utls.VersionTLS12, 0xC02B, /* ECDHE-ECDSA-AES128-GCM-SHA256 (matches the P-256 cert) */
+		ProbeOptions{Timeout: 3 * time.Second, Upgrader: upgrader})
+	if !r.Accepted {
+		t.Fatalf("expected handshake to succeed through upgrader; err=%v", r.Err)
+	}
+	if r.NegotiatedVersion != utls.VersionTLS12 {
+		t.Fatalf("negotiated %#x, want %#x", r.NegotiatedVersion, utls.VersionTLS12)
+	}
+	if err := <-srvDone; err != nil {
+		t.Logf("fake server done with: %v", err) // accept clean close from utls
+	}
+}
+
+func TestProbe_UpgraderError(t *testing.T) {
+	ln, err := net.Listen("tcp", "127.0.0.1:0")
+	if err != nil {
+		t.Fatalf("listen: %v", err)
+	}
+	defer ln.Close()
+	go func() {
+		c, _ := ln.Accept()
+		if c != nil {
+			c.Close()
+		}
+	}()
+
+	wantErr := errors.New("plaintext refused starttls")
+	r := Probe(context.Background(), ln.Addr().String(), "x",
+		utls.VersionTLS12, 0xC02F,
+		ProbeOptions{Timeout: 2 * time.Second, Upgrader: func(net.Conn) error { return wantErr }})
+	if r.Accepted {
+		t.Fatalf("expected probe to fail when upgrader returns error")
+	}
+	if r.Err == nil || !errors.Is(r.Err, wantErr) {
+		t.Fatalf("expected wrapped upgrader error, got %v", r.Err)
+	}
+}
+
+func TestVersionName(t *testing.T) {
+	cases := map[uint16]string{
+		utls.VersionTLS10: "TLS 1.0",
+		utls.VersionTLS11: "TLS 1.1",
+		utls.VersionTLS12: "TLS 1.2",
+		utls.VersionTLS13: "TLS 1.3",
+		0x9999:            "0x9999",
+	}
+	for v, want := range cases {
+		if got := VersionName(v); got != want {
+			t.Errorf("VersionName(%#x) = %q, want %q", v, got, want)
+		}
+	}
+}