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 https://tersign.ai

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

npx tersign verify <receipt.json | 0xdigest> [--ledger url] recovers the EIP-712 signature locally, then checks the entry against the public chain — yours or anyone's. Prefer raw HTTP? The same proof, no CLI:

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

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.

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:

| Capability | In the record | |---|---| | Receipts | Seller-signed EIP-712 (x402 offer-receipt extension), keccak256 canonical digests | | withAssure() | x402 fetch-handler adapter — a receipt per paid call | | Compliance records | EU Art-226b minimal tier · EN 16931 full tier · HK IRO s.51C retention | | Action records | ActionRecordV1 — GDPR-minimized, EU AI Act Art-50 mapped (Art 50 binds 2026-08-02) | | Refunds | Chained to the original receipt via refundOf | | Disputes v0 | Objective reason codes, evidence submission, adjudication | | Venue envelopes | Internet Court (5,000-char slot) · Kleros ERC-1497 · UMA · generic | | Evidence packs | format=art50 · format=safr (beta) | | Idempotency | In-memory + Cloudflare D1 stores |

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_refund · open_dispute · submit_dispute_evidence · adjudicate_dispute · get_dispute

| Env var | Required | Purpose | |---|---|---| | TERSIGN_SELLER_KEY | yes | 0x-prefixed private key that signs your receipts and records | | TERSIGN_LEDGER_URL | no | hosted ledger for counter-signing + chain checks | | TERSIGN_LEDGER_API_KEY | no | your seller API key on that ledger | | TERSIGN_LEDGER_SELLER_ID | no | your seller id on that ledger | | TERSIGN_ISSUER_NAME | no | issuer name stamped on compliance records | | TERSIGN_ISSUER_JURISDICTION | no | issuer jurisdiction stamped on compliance records |

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 — 2,500+ hash-chained observations across 1,100+ x402 seller endpoints, probed hourly and autonomously. Live counts: https://prober.tersign.ai/v1/prober/stats
• Conformance — RFC 8785 (JCS) canonical serialization, keccak256 digests, byte-level cross-implementation vectors published in-repo. Reproduce the bytes and your implementation is conformant — in any language.
• Standards — the compliance-fields extension (optional tax/audit records composing with offer-receipt) is proposed upstream: x402-foundation/x402#2853

Machine Surfaces

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

| Surface | Address | |---|---| | npm package | tersign — https://www.npmjs.com/package/tersign | | MCP registry | io.github.tersignhq/evidence | | ARD catalog (Agentic Resource Discovery) | https://tersign.ai/.well-known/ai-catalog.json | | Verify API | GET https://tersign.ai/v1/receipts/{digest}/verify | | Envelope API | GET https://tersign.ai/v1/receipts/{digest}/envelope?venue={internet-court\|kleros\|uma\|generic} | | Ledger stats | GET https://tersign.ai/v1/stats | | Ledger signer | GET https://tersign.ai/v1/ledger | | llms.txt | https://raw.githubusercontent.com/tersignhq/tersign-js/main/llms.txt | | Conformance vectors (RFC 8785 + keccak256) | https://github.com/tersignhq/tersign-js/blob/main/test/fixtures/canonical-vectors.json | | Sample compliance record + digests | https://github.com/tersignhq/tersign-js/blob/main/test/fixtures/compliance-record.json | | Genesis verify | npx tersign verify 0xe5874f1ffe87f0a6dd9eb157730f67b86ee4538b125fe30fcc4e165213dd3fc4 --ledger https://tersign.ai |