diff --git a/src/cosmosmesh_privacy_preserving_federated/contracts.py b/src/cosmosmesh_privacy_preserving_federated/contracts.py
new file mode 100644
index 0000000..1f05339
--- /dev/null
+++ b/src/cosmosmesh_privacy_preserving_federated/contracts.py
@@ -0,0 +1,155 @@
+"""Contracts and registry scaffolding for CosmosMesh MVP.
+
+This module provides lightweight data-contract primitives used by the
+privacy-preserving federated planning MVP. The goal is to offer a minimal,
+well-typed surface to express LocalProblem data, shared/delta signals, and
+auditability metadata that can be exchanged between agents.
+"""
+from __future__ import annotations
+
+from dataclasses import dataclass, asdict
+from typing import Any, Dict, Optional
+import json
+
+
+@dataclass
+class LocalProblem:
+    """Represents a per-agent optimization problem contract.
+
+    - agent_id: unique identifier for the agent
+    - variables: mapping of variable names to current values (e.g., decision vars)
+    - objective: a simple representation of the objective (coefficients or metadata)
+    - constraints: opaque dict describing constraints (kept generic for MVP)
+    - version: optional version of the contract for auditing
+    """
+
+    agent_id: str
+    variables: Dict[str, float]
+    objective: Dict[str, float]
+    constraints: Dict[str, Any]
+    version: Optional[str] = None
+
+    def to_json(self) -> str:
+        return json.dumps(asdict(self))
+
+    @staticmethod
+    def from_json(payload: str) -> "LocalProblem":
+        data = json.loads(payload)
+        return LocalProblem(**data)  # type: ignore[arg-type]
+
+
+@dataclass
+class SharedVariables:
+    """Container for signals shared across agents (e.g., primal variables)."""
+
+    variables: Dict[str, float]
+    version: Optional[str] = None
+
+    def to_json(self) -> str:
+        return json.dumps(asdict(self))
+
+    @staticmethod
+    def from_json(payload: str) -> "SharedVariables":
+        data = json.loads(payload)
+        return SharedVariables(**data)  # type: ignore[arg-type]
+
+
+@dataclass
+class DualVariables:
+    """Dual variables carried alongside shared variables."""
+
+    values: Dict[str, float]
+    version: Optional[str] = None
+
+    def to_json(self) -> str:
+        return json.dumps(asdict(self))
+
+    @staticmethod
+    def from_json(payload: str) -> "DualVariables":
+        data = json.loads(payload)
+        return DualVariables(**data)  # type: ignore[arg-type]
+
+
+@dataclass
+class PlanDelta:
+    """Represents a delta/patch to a previously computed plan."""
+
+    agent_id: str
+    delta: Dict[str, Any]
+    version: Optional[str] = None
+
+    def to_json(self) -> str:
+        return json.dumps(asdict(self))
+
+    @staticmethod
+    def from_json(payload: str) -> "PlanDelta":
+        data = json.loads(payload)
+        return PlanDelta(**data)  # type: ignore[arg-type]
+
+
+@dataclass
+class PrivacyBudget:
+    """Minimal privacy budget descriptor for local-dp/shared signals."""
+
+    budget: float
+    spent: float = 0.0
+    version: Optional[str] = None
+
+    def to_json(self) -> str:
+        return json.dumps(asdict(self))
+
+    @staticmethod
+    def from_json(payload: str) -> "PrivacyBudget":
+        data = json.loads(payload)
+        return PrivacyBudget(**data)  # type: ignore[arg-type]
+
+
+@dataclass
+class AuditLog:
+    """Auditable event payload used for replay protection and tracing."""
+
+    event: str
+    metadata: Dict[str, Any]
+    timestamp: float
+    version: Optional[str] = None
+
+    def to_json(self) -> str:
+        return json.dumps(asdict(self))
+
+    @staticmethod
+    def from_json(payload: str) -> "AuditLog":
+        data = json.loads(payload)
+        return AuditLog(**data)  # type: ignore[arg-type]
+
+
+class GraphOfContracts:
+    """A tiny registry that maps contract names to versioned schemas.
+
+    This is intentionally lightweight and intended for MVP scaffolding. It
+    allows registering known contract names with a version string and
+    retrieving their canonical representation. The actual schema registry would
+    be a separate service in a full implementation.
+    """
+
+    def __init__(self) -> None:
+        self._registry: Dict[str, str] = {}
+
+    def register(self, name: str, version: str) -> None:
+        self._registry[str(name)] = str(version)
+
+    def get_version(self, name: str) -> Optional[str]:
+        return self._registry.get(name)
+
+    def to_json(self) -> str:
+        return json.dumps(self._registry)
+
+
+__all__ = [
+    "LocalProblem",
+    "SharedVariables",
+    "DualVariables",
+    "PlanDelta",
+    "PrivacyBudget",
+    "AuditLog",
+    "GraphOfContracts",
+]
diff --git a/tests/contracts_test.py b/tests/contracts_test.py
new file mode 100644
index 0000000..b7bc0b6
--- /dev/null
+++ b/tests/contracts_test.py
@@ -0,0 +1,32 @@
+import json
+import time
+
+from cosmosmesh_privacy_preserving_federated.contracts import LocalProblem, GraphOfContracts
+
+
+def test_local_problem_json_roundtrip():
+    lp = LocalProblem(
+        agent_id="rover-1",
+        variables={"x": 1.0, "y": 2.0},
+        objective={"coef": 0.5},
+        constraints={"type": "ineq", "limit": 10.0},
+        version="v0.1",
+    )
+    payload = lp.to_json()
+    lp2 = LocalProblem.from_json(payload)
+    assert lp2.agent_id == lp.agent_id
+    assert lp2.variables == lp.variables
+    assert lp2.version == lp.version
+
+
+def test_graph_of_contracts_registry():
+    g = GraphOfContracts()
+    g.register("LocalProblem", "v0.1")
+    g.register("PlanDelta", "v0.2")
+    assert g.get_version("LocalProblem") == "v0.1"
+    assert g.get_version("PlanDelta") == "v0.2"
+    # ensure JSON export works and is parseable
+    data = g.to_json()
+    assert isinstance(data, str)
+    parsed = json.loads(data)
+    assert "LocalProblem" in parsed