diff --git a/gravityweave/receipt.py b/gravityweave/receipt.py
new file mode 100644
index 0000000..c14b473
--- /dev/null
+++ b/gravityweave/receipt.py
@@ -0,0 +1,103 @@
+"""Mutual Feasibility Receipt (MFR).
+
+Small, signed receipts produced in response to a PlanDelta synopsis/proposal
+that state which invariants the responder believes are satisfied for a given
+custody window. The receipt is deliberately compact and uses an HMAC-based
+signature for tests/poC; production would use DID-based signatures.
+
+Fields:
+- receipt_id: short random id
+- proposal_hash: short digest of the proposal (e.g., delta summary_hash)
+- invariant_ids: list of small invariant identifiers (strings)
+- decision: one of "ok", "partial", "deny"
+- uncertainty: float 0..1 expressing uncertainty (0 = certain)
+- round_nonce: numeric round to prevent replay
+- ts: timestamp
+- sig: HMAC signature over canonical payload
+
+"""
+from dataclasses import dataclass, field
+from typing import List, Dict, Any, Optional
+import time
+import uuid
+import json
+import hmac
+import hashlib
+
+
+@dataclass
+class MutualFeasibilityReceipt:
+    receipt_id: str
+    proposal_hash: str
+    invariant_ids: List[str]
+    decision: str
+    uncertainty: float
+    round_nonce: int
+    ts: float
+    signer: str = ""
+    sig: str = ""
+
+    @classmethod
+    def create(cls, proposal_hash: str, invariant_ids: List[str], decision: str,
+               uncertainty: float = 0.0, round_nonce: int = 0, signer: str = "",
+               key: Optional[bytes] = None) -> "MutualFeasibilityReceipt":
+        rid = uuid.uuid4().hex[:12]
+        ts = time.time()
+        r = cls(receipt_id=rid, proposal_hash=proposal_hash,
+                invariant_ids=invariant_ids, decision=decision,
+                uncertainty=float(uncertainty), round_nonce=int(round_nonce), ts=ts,
+                signer=signer, sig="")
+        if key:
+            r.sig = r._sign(key)
+        return r
+
+    def _canonical_payload(self) -> str:
+        # deterministic JSON over the authoritative fields
+        payload = {
+            "receipt_id": self.receipt_id,
+            "proposal_hash": self.proposal_hash,
+            "invariant_ids": self.invariant_ids,
+            "decision": self.decision,
+            "uncertainty": round(self.uncertainty, 6),
+            "round_nonce": self.round_nonce,
+            "ts": int(self.ts),
+            "signer": self.signer,
+        }
+        return json.dumps(payload, sort_keys=True, separators=(",", ":"))
+
+    def _sign(self, key: bytes) -> str:
+        payload = self._canonical_payload()
+        return hmac.new(key, payload.encode("utf-8"), hashlib.sha256).hexdigest()
+
+    def verify(self, key: bytes) -> bool:
+        if not self.sig:
+            return False
+        expected = self._sign(key)
+        return hmac.compare_digest(expected, self.sig)
+
+    def serialize(self) -> bytes:
+        obj = {
+            "receipt_id": self.receipt_id,
+            "proposal_hash": self.proposal_hash,
+            "invariant_ids": self.invariant_ids,
+            "decision": self.decision,
+            "uncertainty": self.uncertainty,
+            "round_nonce": self.round_nonce,
+            "ts": self.ts,
+            "signer": self.signer,
+            "sig": self.sig,
+        }
+        return json.dumps(obj, sort_keys=True, separators=(",", ":")).encode("utf-8")
+
+    @classmethod
+    def deserialize(cls, b: bytes) -> "MutualFeasibilityReceipt":
+        obj = json.loads(b.decode("utf-8"))
+        return cls(receipt_id=obj.get("receipt_id", ""),
+                   proposal_hash=obj.get("proposal_hash", ""),
+                   invariant_ids=obj.get("invariant_ids", []),
+                   decision=obj.get("decision", "deny"),
+                   uncertainty=float(obj.get("uncertainty", 0.0)),
+                   round_nonce=int(obj.get("round_nonce", 0)),
+                   ts=float(obj.get("ts", 0.0)),
+                   signer=obj.get("signer", ""),
+                   sig=obj.get("sig", ""))
diff --git a/tests/test_receipt.py b/tests/test_receipt.py
new file mode 100644
index 0000000..d46c276
--- /dev/null
+++ b/tests/test_receipt.py
@@ -0,0 +1,39 @@
+from gravityweave.receipt import MutualFeasibilityReceipt
+
+
+def test_receipt_create_and_verify():
+    key = b"node-secret"
+    prop_hash = "deadbeefcafebabe"
+    invariants = ["fuel_bound", "power_bound"]
+
+    r = MutualFeasibilityReceipt.create(proposal_hash=prop_hash,
+                                        invariant_ids=invariants,
+                                        decision="ok",
+                                        uncertainty=0.1,
+                                        round_nonce=1,
+                                        signer="nodeA",
+                                        key=key)
+
+    assert r.proposal_hash == prop_hash
+    assert r.decision == "ok"
+    assert r.verify(key) is True
+
+    ser = r.serialize()
+    # ensure compact size under 512 bytes
+    assert len(ser) <= 512
+
+    r2 = MutualFeasibilityReceipt.deserialize(ser)
+    assert r2.receipt_id == r.receipt_id
+    # verify with same key
+    assert r2.verify(key) is True
+
+
+def test_receipt_tamper_detection():
+    key = b"k"
+    r = MutualFeasibilityReceipt.create(proposal_hash="h", invariant_ids=["i"], decision="ok",
+                                        signer="s", key=key)
+    ser = r.serialize()
+    # tamper with serialized bytes
+    s2 = ser.replace(b"ok", b"deny")
+    r2 = MutualFeasibilityReceipt.deserialize(s2)
+    assert r2.verify(key) is False