For Developers

Build your own implementation

The barter.game protocol is intentionally small. You can read the full contract in an afternoon. The reference implementation is TypeScript + Deno Deploy, but the protocol does not care what language or stack you use.

The invariant contract

Read the protocol/ spec first. It defines:

• The document types: Voucher, Account, Order, Mandate, Record, Offer, Signature, Subscription, Address — Records are bank-minted and identified by ULID
• RFC 8785 canonical JSON (cross-runtime parity is load-bearing)
• ed25519 signatures over SHA-256 hashes
• The JSON-RPC envelope and replay protection
• Coordinator-orchestrated approval: each holder signs their own Order (lead/follow), a coordinator creates the records and clears each Order with a signed Mandate, and the banks self-advance with a lead-first settle cascade
• The state machine (created → approved → held → settled / rejected)
• The concurrency invariants (sum-to-zero, one active hold per account)

Everything in that file is the contract. Change it and you are no longer speaking barter.game v1.

What you CAN change

See the reference implementation notes for how the reference team made each choice and what alternatives you might consider.

Quickstart checklist

If you’re building a bank from scratch:

1. Implement RFC 8785 canonical JSON. Verify cross-runtime parity.
2. Implement ed25519 sign/verify and SHA-256. Use audited libraries.
3. Define the doc types and their validators.
4. Build the JSON-RPC envelope handler with replay protection.
5. Implement submit_docs, create_records, submit_mandate, subscribe, notify_signatures, get_record_signatures, and the read methods (get_voucher, get_balance, list_accounts, list_account_records, list_offers, …).
6. Implement the advance engine: records self-advance created → approved → held → settled, evaluated on every incoming signature.
7. Enforce sum-to-zero on every settle.
8. Enforce at most one active hold per account.
9. Expose GET /<name>/barter-bank.json (and GET /<name>/address/<pubkey> if you want an address directory).
10. Write a client that can run a trade end-to-end (publish Orders → discover Offers → create records → mandate → banks settle), bilateral or N-party.
11. Run it against the reference banks to verify interop.

The protocol library

The reference packages/protocol/ is MIT-licensed, dependency-light, and a single source file — src/index.ts. It runs under Bun, Deno, and browser. You can import it directly or treat it as the spec to port:

Read more

• Invariant protocol contract →
• Reference bank server →
• Reference web client →
• Source code →