diff --git a/deltatrace/capture.py b/deltatrace/capture.py
new file mode 100644
index 0000000..5f6e1fd
--- /dev/null
+++ b/deltatrace/capture.py
@@ -0,0 +1,76 @@
+"""Capture utilities for reproducible trace envelopes.
+
+Provides a small helper to bundle a serialized event-graph snapshot with
+immutable runtime metadata so a trace can be archived and later replayed
+in a self-contained manner.
+"""
+
+from __future__ import annotations
+
+import json
+import platform
+import time
+from dataclasses import dataclass
+from typing import Any, Dict, Optional
+
+
+@dataclass
+class ReproducibleEnvelope:
+    """A self-contained capture bundle for deterministic replays.
+
+    Fields intentionally minimal: snapshot (event graph), adapters metadata,
+    deterministic seeds, runtime snapshot (python/platform), and a CLI/config
+    snapshot string.
+    """
+
+    snapshot: Dict[str, Any]
+    adapters: Dict[str, str]
+    rng_seed: Optional[int]
+    container_image: Optional[str]
+    cmdline: Optional[str]
+    timestamp_ns: int
+    runtime: Dict[str, str]
+
+    def to_dict(self) -> Dict[str, Any]:
+        return {
+            "snapshot": self.snapshot,
+            "adapters": self.adapters,
+            "rng_seed": self.rng_seed,
+            "container_image": self.container_image,
+            "cmdline": self.cmdline,
+            "timestamp_ns": self.timestamp_ns,
+            "runtime": self.runtime,
+        }
+
+
+def create_reproducible_envelope(
+    snapshot: Dict[str, Any],
+    adapters: Optional[Dict[str, str]] = None,
+    rng_seed: Optional[int] = None,
+    container_image: Optional[str] = None,
+    cmdline: Optional[str] = None,
+) -> ReproducibleEnvelope:
+    """Create a reproducible envelope bundling snapshot + metadata.
+
+    This is deliberately lightweight: callers should pass adapter version
+    strings (e.g. package@version or binary digest) and any available
+    runtime metadata. The envelope is JSON-serializable via `to_dict()`.
+    """
+
+    adapters = adapters or {}
+    return ReproducibleEnvelope(
+        snapshot=snapshot,
+        adapters=adapters,
+        rng_seed=rng_seed,
+        container_image=container_image,
+        cmdline=cmdline,
+        timestamp_ns=time.time_ns(),
+        runtime={
+            "python": platform.python_version(),
+            "platform": platform.platform(),
+        },
+    )
+
+
+def envelope_to_json(env: ReproducibleEnvelope) -> str:
+    return json.dumps(env.to_dict(), sort_keys=True)
diff --git a/tests/test_capture.py b/tests/test_capture.py
new file mode 100644
index 0000000..427887c
--- /dev/null
+++ b/tests/test_capture.py
@@ -0,0 +1,25 @@
+from deltatrace.capture import create_reproducible_envelope, envelope_to_json
+from deltatrace.event_graph import Event, EventType, EventGraph
+from deltatrace.replay_engine import ReplayEngine
+
+
+def test_reproducible_envelope_contains_snapshot_and_replays():
+    g = EventGraph()
+    t1 = Event.create(EventType.MD_TICK, {"v": 1})
+    s1 = Event.create(EventType.SIGNAL, {"v": 2})
+    g.add_event(t1)
+    g.add_event(s1)
+    g.add_edge(t1.id, s1.id)
+
+    # create checkpoint/snapshot
+    snapshot = g.to_dict()
+
+    env = create_reproducible_envelope(snapshot, adapters={"fix": "fix-adapter@0.1"}, rng_seed=42, container_image="sha256:deadbeef", cmdline="demo --run")
+
+    j = envelope_to_json(env)
+    assert isinstance(j, str) and 'snapshot' in j
+
+    # replay from snapshot inside envelope
+    engine = ReplayEngine()
+    res = engine.replay_from_snapshot(env.snapshot)
+    assert res.events_replayed == len(g.events)