The gap
x402 already solves payment. Settlement on Stellar works today. The gap is discovery: an agent can only pay an endpoint it already knows about. Rialto adds the discovery layer, so a payment settling through the facilitator is what catalogs the service it paid for.
What ships
Canonical /verify, /settle, /supported, built on the Apache-2.0 @x402/stellar package. We compose settlement, we do not reimplement it.
Postgres-backed catalog with hybrid search and settlement-history ranking, so agents can tell proven endpoints from stale ones.
Independent facilitators register. External catalogs are ingested and cross-published.
Settles anywhere. Findable everywhere.
Proof, not claims
Public eval harness
@rialto/eval-harness is a versioned golden-query set scored on nDCG@10, MRR, and Recall@20, gated in CI on every ranking change, re-runnable by anyone.
Validated at the source
Malformed listings are a real, observed problem in production catalogs. @rialto/seller-sdk validates discovery metadata locally, before it ever reaches an index.
How it works
Seller declares
Metadata declared and validated locally via seller-sdk.
Payment settles
The facilitator verifies and settles the x402 payment on Stellar.
Bazaar catalogs it
Settlement carrying the Bazaar extension indexes the service automatically.
Agent discovers + pays
Via MCP search_resources / paid_call.
Design decisions
ADR 0001: upto on-chain cap
“Token allowances alone cannot bind the recipient or guarantee single settlement.”
A minimal, stateless Soroban contract enforces the spending cap on-chain and settles atomically in one transaction.
Read ADR 0001 ↗ADR 0002: search stack
Rejected Elasticsearch for license reasons, and a dedicated vector database as “a second stateful service for a corpus that fits in RAM.”
Hybrid retrieval runs on plain PostgreSQL instead: one boring, self-hostable store.
Read ADR 0002 ↗Prior work
AgentVault
Verifiable storage infrastructure for autonomous AI agents: Filecoin Onchain Cloud, x402 micropayments, and ERC-8004 identity, so an agent can prove who it is and that its stored data is real, not just that it paid for storage.
FCR-x402
An x402 facilitator for Filecoin using the Fast Confirmation Rule for sub-minute finality, with instant EIP-3009 payments and a deferred escrow model for high-frequency calls, both backed by facilitator-posted USDFC collateral.
Code lands in the open.