Evidence

Tersign is the evidence layer for the agent economy — a neutral, counter-signed, hash-chained ledger for agent commerce. Sellers sign EIP-712 receipts; Tersign chains them per seller and counter-signs every entry. When the dispute comes, the transcript is already sealed.

Venues rotate. The transcript endures.

Verify a Real Entry — Right Now

No account. No API key. This is the genesis receipt, seq 1 on the production chain:

npx tersign verify 0xe5874f1ffe87f0a6dd9eb157730f67b86ee4538b125fe30fcc4e165213dd3fc4

ledger: counter-signed OK (seller tersign-first, seq 1 …) VALID

npx tersign verify <receipt.json | 0xdigest> [--ledger url] recovers the EIP-712 signature locally. A bare digest is then checked against the Tersign ledger unless --ledger names another; a receipt file verifies offline and touches no chain at all. The ledger consulted is always printed. Prefer raw HTTP? The same proof, no CLI:

curl https://tersign.ai/v1/receipts/0xe5874f1ffe87f0a6dd9eb157730f67b86ee4538b125fe30fcc4e165213dd3fc4/verify

One-Call Disclosure Evidence

Counter-signed evidence that your agent presented a disclosure — one command, no account:

npx tersign disclose "You are chatting with an AI assistant." --medium chat --agent-id my-agent

The text is digested locally (only the digest travels — data-minimization by construction). Your key signs the record; the ledger counter-signs it into a per-signer hash chain whose head is submitted for Bitcoin anchoring on a six-hourly cron. First call self-provisions a free signer-keyed account bound set-once to your key (key resolution: TERSIGN_SELLER_KEY env → macOS keychain tersign-signer → ~/.tersign/signer.key, created on first use). Free tier is quota- and rate-limited — limits. What this is: independently verifiable evidence the disclosure was attested at that time. What it is not: a compliance certification.

Chain of Custody

Every entry takes the same path: the seller signs the receipt (EIP-712, x402 offer-receipt extension) → Tersign computes the keccak256 canonical digest → the digest joins that seller's hash chain, each seq n bound to seq n−1 → the neutral ledger counter-signs (secp256k1) → anyone verifies, and any venue gets a serialized envelope.

Since 2026-08-28 each anchor stamps a chain commitment — an accumulator over every counter-signed link — so one anchored digest covers the whole prefix; rows anchored earlier bind the head record only and say so (subjectSchema).

graph LR
    A["agent transaction<br/>x402"] --> B["seller-signed receipt<br/>EIP-712"]
    B --> C["canonical digest<br/>keccak256"]
    C --> D["per-seller hash chain<br/>seq n binds seq n−1"]
    D --> E["neutral counter-signature<br/>secp256k1 ledger"]
    E --> F["verifiable by anyone<br/>venue-ready envelope"]

_{Diagram renders on GitHub. On npm, the paragraph above IS the diagram.}

Refunds chain back to the original receipt via refundOf. Disputes attach to the digest with objective reason codes. Party statements are structurally segregated behind an UNVERIFIED marker — the evidence stays prompt-injection-hardened.

Enter the Record

npm i tersign

withAssure() wraps your x402 fetch handler so every paid call issues a signed, chained receipt. The full register:

Capture at the MCP Boundary — tersign intercept

An agent's tool calls are usually recorded, if at all, by the party running the agent. Put a recording clamp on the wire instead:

npx tersign intercept -- npx your-mcp-server

The proxy is a pure observer: bytes reach the server and the client exactly as sent, in order, unmodified. Every tools/call it sees becomes an ActionRecordV1 signed by your key and counter-signed into a hash chain — digests only, so the record proves what happened without carrying arguments or results anywhere. Records go to a configured ledger, and fall back to a local ~/.tersign/intercepts-<date>.jsonl so evidence is never silently dropped.

Experimental, and deliberately unopinionated about where the protocol lands: it implements the observation semantics of the audit-mode validator described in MCP SEP-2624 (Draft) as a transport-level proxy today, and is structured to move onto the interceptor primitive if and when that stabilizes. It makes no conformance claim to that draft.

For Agents — the MCP Server

npx tersign starts the MCP server (stdio). Official registry entry: io.github.tersignhq/evidence (active).

{
  "mcpServers": {
    "tersign": {
      "command": "npx",
      "args": ["tersign"],
      "env": { "TERSIGN_SELLER_KEY": "0x<your-seller-key>" }
    }
  }
}

Tools — issue_receipt · verify_receipt · verify_compliance_record · record_disclosure · record_refund · open_dispute · submit_dispute_evidence · adjudicate_dispute · get_dispute

Cold to counter-signed in one session: call issue_receipt, then check the issued receipt's digest with npx tersign verify <digest> --ledger <url>.

The agent skill tersign-evidence ships at tersignhq/skills.

The Live Record

• Ledger + dashboard — public verify page: https://tersign.ai/verify
• Census — hash-chained observations across the live x402 seller catalog, probed autonomously; the numbers are served live, never quoted stale: https://prober.tersign.ai/v1/prober/stats
• Conformance — RFC 8785 (JCS) canonical serialization, keccak256 digests, and the public two-sided vector suite (canonical bytes, number domain, content address, chain continuity, completeness, anchored existence, phase separation, offer binding, independence — every criterion carrying both an accepting and an adversarial vector): tersignhq/evidence-record-conformance. Reproduce the bytes and your implementation is conformant — in any language.
• Standards — the compliance-fields extension — a typed compliance-record schema plus four evaluator-side disqualifications (independence, completeness/existence, economic-phase separation, and commitment scope — an independence claim reaches exactly as far as the record's own commitments), each executable as a two-sided conformance vector — is under review upstream (x402-foundation/x402#2853) and referenced in the x402 TSC's evidence-record charter agenda (tsc#4). The merged offer-receipt spec already carries post-session verification guidance — signer authorization evaluated as of issuedAt, with mutable-source rotation handled explicitly (#2811, merged); the completeness, independence, existence and phase disqualifications are the open extension's normative core.

Machine Surfaces

Full URLs, readable without auth. If you are an agent, start here.