Receipts, or it didn't happen.

Sentinel turns every action — human or AI — into a hash-chained, tamper-evident receipt. There are only two verbs to learn: seal an action, and verify the chain. Everything else is detail.

01 Quickstart

From a key to your first sealed receipt in five minutes.

1. Get a key. Founding Partners receive a workspace key. Set it in your environment as SENTINEL_KEY.
2. Seal your first action. One POST. Humans and agents use the same call.
3. Verify. Re-check the chain — no key needed.

# seal an action
curl -X POST https://sentinel.matchain.io/v1/receipts \
  -H "Authorization: Bearer $SENTINEL_KEY" \
  -d '{"operator":"agent:planner-7","role":"planner",
       "action":"deploy","target":"svc/checkout@1.9.2","scope":"ok"}'
→ { "seq":1069, "hash":"a1f0…e9", "prev":"9c4b…2d" }

# verify the whole chain — no key required
curl https://sentinel.matchain.io/v1/verify
→ { "ok":true, "links":1069, "root":"0x9f4c…e21" }

# pip install sentinel-sdk
from sentinel import Sentinel

s = Sentinel(api_key=os.environ["SENTINEL_KEY"])

r = s.receipts.seal(
    operator="agent:planner-7", role="planner",
    action="deploy", target="svc/checkout@1.9.2", scope="ok",
)
print(r.seq, r.hash)

v = s.verify()
assert v.ok, f"broken at #{v.broken_at}"

// npm i @sentinel/sdk
import { Sentinel } from "@sentinel/sdk";

const s = new Sentinel({ apiKey: process.env.SENTINEL_KEY });

const r = await s.receipts.seal({
  operator: "agent:planner-7", role: "planner",
  action: "deploy", target: "svc/checkout@1.9.2", scope: "ok",
});
console.log(r.seq, r.hash);

const v = await s.verify();
if (!v.ok) throw new Error(`broken at #${v.brokenAt}`);

02 Authentication

Sealing receipts is authenticated with a workspace key. Verifying is not — integrity is public by design.

• Bearer key. Send your key as Authorization: Bearer SENTINEL_KEY on every write. Keys are workspace-scoped; one key can emit for many operators and agents.
• Keyless verify. GET /v1/verify needs no credentials. A regulator, a partner, or a stranger can re-check your chain at any time — that is the point.
• Rotate freely. Issue and revoke keys per workspace. A revoked key cannot seal new receipts; receipts it already sealed stay valid and attributable.
• Never the content. A key authorizes sealing metadata, never reading your underlying data. Sentinel sells proof of integrity, not access.

03 Receipts API

Two endpoints carry the whole surface. Everything is JSON over HTTPS.

Request body fields:

Returns { "ok": true, "links": N, "root": "0x…" } on a clean chain, or { "ok": false, "broken_at": N } pointing at the first receipt whose hash no longer matches. The root is the Merkle root anchored on-chain on a cadence.

04 Receipt schema

What you get back. The last three fields are what make it tamper-evident.

05 Errors & rate limits

Free tier is 1,000 reads/day. Paid plans raise the ceiling; the Regulated band is bespoke. Regulator access is unlimited and free, forever.

06 SDKs

Thin wrappers over the same two calls. No SDK required — raw HTTP works from anywhere.

# pip install sentinel-sdk
from sentinel import Sentinel
s = Sentinel(api_key=KEY)
s.receipts.seal(operator="u:ana", role="ops",
                action="payout", target="inv:4821")

// npm i @sentinel/sdk
import { Sentinel } from "@sentinel/sdk";
const s = new Sentinel({ apiKey: KEY });
await s.receipts.seal({ operator: "u:ana",
  role: "ops", action: "payout", target: "inv:4821" });

// go get sentinel.sh/go
s := sentinel.New(KEY)
s.Receipts.Seal(sentinel.Action{
  Operator: "u:ana", Role: "ops",
  Action: "payout", Target: "inv:4821",
})

07 Concepts

The architecture, in plain terms — the public half of the whitepaper. No secret sauce, just the load-bearing ideas.