diff --git a/.gitattributes b/.gitattributes
index bdd0de2..a06270a 100644
--- a/.gitattributes
+++ b/.gitattributes
@@ -1,2 +1,3 @@
 * text=auto eol=lf
 *.go text eol=lf
+msgpack-test-suite.json -text
diff --git a/msgpack-test-suite.json b/msgpack-test-suite.json
new file mode 100644
index 0000000..b688e30
--- /dev/null
+++ b/msgpack-test-suite.json
@@ -0,0 +1,722 @@
+{
+ "10.nil.yaml": [
+  {
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+   "msgpack": [
+    "c0"
+   ]
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+ ],
+ "11.bool.yaml": [
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+   "msgpack": [
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+   ]
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+  {
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+   "msgpack": [
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+    "d3-00-00-00-00-ff-ff-ff-ff",
+    "cb-41-ef-ff-ff-ff-e0-00-00"
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+    "d1-ff-ff",
+    "d2-ff-ff-ff-ff",
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+    "cb-3f-e0-00-00-00-00-00-00"
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+   "bignum": "4294967296",
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+ "30.string-ascii.yaml": [
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+   "string": "",
+   "msgpack": [
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+    "d9-00",
+    "da-00-00",
+    "db-00-00-00-00"
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+    "d9-01-61",
+    "da-00-01-61",
+    "db-00-00-00-01-61"
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+  },
+  {
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+    "d9-1f-31-32-33-34-35-36-37-38-39-30-31-32-33-34-35-36-37-38-39-30-31-32-33-34-35-36-37-38-39-30-31",
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+    "da-00-20-31-32-33-34-35-36-37-38-39-30-31-32-33-34-35-36-37-38-39-30-31-32-33-34-35-36-37-38-39-30-31-32"
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+   "msgpack": [
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+   "msgpack": [
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+    "d9-0c-e3-81-b2-e3-82-89-e3-81-8c-e3-81-aa"
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+  {
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+   "msgpack": [
+    "a6-ed-95-9c-ea-b8-80",
+    "d9-06-ed-95-9c-ea-b8-80"
+   ]
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+  {
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+   "msgpack": [
+    "a6-e6-b1-89-e5-ad-97",
+    "d9-06-e6-b1-89-e5-ad-97"
+   ]
+  },
+  {
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+   "msgpack": [
+    "a6-e6-bc-a2-e5-ad-97",
+    "d9-06-e6-bc-a2-e5-ad-97"
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+    "d9-03-e2-9d-a4"
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+  {
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+   "msgpack": [
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+    "d9-04-f0-9f-8d-ba"
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+    "dc-00-01-01",
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+   "msgpack": [
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+   ]
+  },
+  {
+   "ext": [ 3,
+    "30-31-32-33"
+   ],
+   "msgpack": [
+    "d6-03-30-31-32-33"
+   ]
+  },
+  {
+   "ext": [ 4,
+    "40-41-42-43-44-45-46-47"
+   ],
+   "msgpack": [
+    "d7-04-40-41-42-43-44-45-46-47"
+   ]
+  },
+  {
+   "ext": [ 5,
+    "50-51-52-53-54-55-56-57-58-59-5a-5b-5c-5d-5e-5f"
+   ],
+   "msgpack": [
+    "d8-05-50-51-52-53-54-55-56-57-58-59-5a-5b-5c-5d-5e-5f"
+   ]
+  },
+  {
+   "ext": [ 6,
+    ""
+   ],
+   "msgpack": [
+    "c7-00-06",
+    "c8-00-00-06",
+    "c9-00-00-00-00-06"
+   ]
+  },
+  {
+   "ext": [ 7,
+    "70-71-72"
+   ],
+   "msgpack": [
+    "c7-03-07-70-71-72",
+    "c8-00-03-07-70-71-72",
+    "c9-00-00-00-03-07-70-71-72"
+   ]
+  }
+ ]
+}
diff --git a/suite_test.go b/suite_test.go
new file mode 100644
index 0000000..b5f605e
--- /dev/null
+++ b/suite_test.go
@@ -0,0 +1,171 @@
+// Copyright (c) the go-ruby-msgpack/msgpack authors
+//
+// SPDX-License-Identifier: BSD-3-Clause
+
+package msgpack
+
+import (
+	_ "embed"
+	"encoding/hex"
+	"encoding/json"
+	"sort"
+	"strings"
+	"testing"
+)
+
+// msgpackTestSuite is the canonical MessagePack conformance corpus
+// kawanet/msgpack-test-suite (dist/msgpack-test-suite.json). It groups the spec's
+// value families (nil/bool/bin/int/float/bignum/str/array/map/nested/timestamp/
+// ext) and, for each value, lists every valid MessagePack byte encoding (the
+// minimal one plus the wider fixint/8/16/32/64 and int-vs-float variants). It is
+// vendored verbatim so this package gates on the reference's own vectors.
+//
+//go:embed msgpack-test-suite.json
+var msgpackTestSuite []byte
+
+// suiteCase is one corpus entry: the type-tagged value fields are ignored here
+// (the round-trip check does not need them) and Encodings holds every dash-
+// separated lowercase-hex encoding the spec sanctions for that value.
+type suiteCase struct {
+	group     string
+	line      int // 1-based index within its group, for a stable ratchet key
+	Encodings []string
+}
+
+// parseSuite decodes the corpus JSON into a flat, ordered list of cases.
+func parseSuite(t *testing.T) []suiteCase {
+	t.Helper()
+	var raw map[string][]map[string]json.RawMessage
+	if err := json.Unmarshal(msgpackTestSuite, &raw); err != nil {
+		t.Fatalf("decode corpus: %v", err)
+	}
+	groups := make([]string, 0, len(raw))
+	for g := range raw {
+		groups = append(groups, g)
+	}
+	sort.Strings(groups)
+	var cases []suiteCase
+	for _, g := range groups {
+		for i, entry := range raw[g] {
+			var encs []string
+			if err := json.Unmarshal(entry["msgpack"], &encs); err != nil {
+				t.Fatalf("%s[%d]: decode msgpack encodings: %v", g, i, err)
+			}
+			cases = append(cases, suiteCase{group: g, line: i + 1, Encodings: encs})
+		}
+	}
+	return cases
+}
+
+// key is the stable ratchet identifier for a case, e.g. "41.map.yaml#2".
+func (c suiteCase) key() string {
+	return c.group + "#" + itoa(c.line)
+}
+
+func itoa(n int) string {
+	if n == 0 {
+		return "0"
+	}
+	var b [20]byte
+	i := len(b)
+	for n > 0 {
+		i--
+		b[i] = byte('0' + n%10)
+		n /= 10
+	}
+	return string(b[i:])
+}
+
+// decodeHex turns a dash-separated lowercase-hex encoding ("de-00-01") into bytes.
+func decodeHex(t *testing.T, s string) []byte {
+	t.Helper()
+	b, err := hex.DecodeString(strings.ReplaceAll(s, "-", ""))
+	if err != nil {
+		t.Fatalf("bad hex %q: %v", s, err)
+	}
+	return b
+}
+
+// encodeHex renders bytes back to the corpus's dash-separated lowercase hex.
+func encodeHex(b []byte) string {
+	parts := make([]string, len(b))
+	for i, x := range b {
+		parts[i] = hex.EncodeToString([]byte{x})
+	}
+	return strings.Join(parts, "-")
+}
+
+// roundTrips reports whether every listed encoding of a case Unpacks without
+// error and re-Packs to a byte string the corpus also lists for that value. This
+// is the MessagePack conformance check: each wide-header / int-vs-float variant
+// must decode, and the decoded value must serialise back to one of the spec's
+// sanctioned encodings (the codec's canonical form).
+func roundTrips(t *testing.T, c suiteCase) bool {
+	set := make(map[string]bool, len(c.Encodings))
+	for _, e := range c.Encodings {
+		set[e] = true
+	}
+	for _, e := range c.Encodings {
+		v, err := Unpack(decodeHex(t, e))
+		if err != nil {
+			return false
+		}
+		out, err := Pack(v)
+		if err != nil {
+			return false
+		}
+		if !set[encodeHex(out)] {
+			return false
+		}
+	}
+	return true
+}
+
+// suiteKnownFailing is the frozen set of msgpack-test-suite cases (keyed by
+// "group#line") this package does not yet round-trip against the spec's
+// sanctioned encodings. It is a shrink-only conformance RATCHET: every case NOT
+// listed here must round-trip, so no change may introduce a new encoding
+// regression, and a listed case that starts passing is reported so the entry can
+// be removed. Baseline captured 2026-08-03.
+var suiteKnownFailing = map[string]bool{}
+
+// TestMsgpackTestSuiteConformance is the differential round-trip gate against the
+// canonical kawanet/msgpack-test-suite corpus. Every case outside
+// suiteKnownFailing must decode all of its listed encodings and re-encode to a
+// spec-sanctioned form; a new failure fails CI and a listed case that now passes
+// is reported so the ratchet can be tightened.
+func TestMsgpackTestSuiteConformance(t *testing.T) {
+	cases := parseSuite(t)
+	if len(cases) < 80 {
+		t.Fatalf("expected ~85 corpus cases, parsed %d", len(cases))
+	}
+	pass, vectors, vectorsPass := 0, 0, 0
+	var newFail, fixed []string
+	for _, c := range cases {
+		ok := roundTrips(t, c)
+		vectors += len(c.Encodings)
+		if ok {
+			pass++
+			vectorsPass += len(c.Encodings)
+		}
+		switch {
+		case ok && suiteKnownFailing[c.key()]:
+			fixed = append(fixed, c.key())
+		case !ok && !suiteKnownFailing[c.key()]:
+			newFail = append(newFail, c.key())
+		}
+	}
+	t.Logf("msgpack-test-suite: %d/%d cases round-trip (%.2f%%), %d/%d encoding "+
+		"vectors, %d known gaps", pass, len(cases), 100*float64(pass)/float64(len(cases)),
+		vectorsPass, vectors, len(suiteKnownFailing))
+	if len(fixed) > 0 {
+		sort.Strings(fixed)
+		t.Errorf("cases now passing that are still listed in suiteKnownFailing: %v\n"+
+			"remove them to tighten the ratchet", fixed)
+	}
+	if len(newFail) > 0 {
+		sort.Strings(newFail)
+		t.Errorf("REGRESSION: %d msgpack-test-suite case(s) that must round-trip now "+
+			"fail: %v", len(newFail), newFail)
+	}
+}