Stellar Community Fund

By Rumble Fish Software Development - RFP

x402 facilitator and Bazaar discovery

SCF #45

$78.0K

Build

Information Collection

Products & Services

An open-source x402 payment facilitator and Bazaar discovery layer for Stellar, letting AI agents find, price, and pay for API endpoints and MCP tools per request in USDC or any SEP-41 asset, at near-zero settlement cost (~0.0023 XLM per transaction). Includes a usage-based ("upto") settlement scheme for metered pricing — proposed upstream to the x402 spec — an MCP-native discovery interface for agent runtimes, and SDK support in both TypeScript and Rust.

Requested Budget

$78.0K

Traction Evidence

Our team operates the Soroban Block Explorer, a live production human-readable transaction and contract explorer for Stellar, delivered under a separate SCF Build Award. We are also currently developing a Prices API (unified price data for classic and Soroban assets) under a second SCF award, on track to ship before this engagement needs to integrate it. Rather than build synthetic demo endpoints for this RFP's required example integrations, we will gate both of these production services behind the x402 facilitator and Bazaar proposed here — giving the infrastructure real, non-trivial production traffic to prove itself against from day one, and directly furthering our own independent monetization plans for both projects. This is concrete evidence of both our SCF delivery track record and our ability to ship production Stellar infrastructure, not a first-time proposal.

Tranche 1 (Deliverable Roadmap) - MVP

[Deliverable 1] Foundation

Facilitator hardened and live on stellar:testnet: verify/settle/supported endpoints, any SEP-41 token accepted, sponsored fees, rate limiting documented. Bazaar resources endpoint and cataloging pipeline live on testnet (ranking not yet enabled). upto scheme design finalized; proxy contract deployed to testnet (pre-audit) with passing unit tests for ceiling/nonce/expiry enforcement. TypeScript SDK helpers and Rust seller crate scaffolding in progress. Core test suite skeleton in place.

How to measure completion: Testnet facilitator responds correctly to verify/settle/supported per the x402 v2 spec for at least one SEP-41 asset; GET /discovery/resources returns a correctly-shaped catalog entry for a seeded test resource; upto proxy contract deployed to testnet with a documented test suite covering ceiling enforcement, expiry, and single-use nonce consumption; a published design note for scheme_upto_stellar.md.

Budget: $15,600

Tranche 2 (Deliverable Roadmap) - Testnet

[Deliverable 2] Feature Complete

Bazaar search endpoint live with ranking (relevance + quality score + curation) on testnet. MCP discovery server functional (search + paid-call tools). scheme_upto_stellar.md submitted to the x402 Technical Steering Committee. TypeScript SDK and Rust seller crate both feature complete. Facilitator live on stellar:pubnet. External security audit engaged and underway. Prices API and Block Explorer API both payment-gated on testnet using the new Rust crate.

How to measure completion: GET /discovery/search returns ranked results for a natural language query against at least 3 seeded resources, with documented ranking signals; MCP server responds to a search-then-pay tool call end to end on testnet; TSC submission of scheme_upto_stellar.md is publicly visible (PR or discussion thread); Prices API and Block Explorer API both return 402 responses with valid payment terms on testnet and complete a settled payment end to end using the Rust crate; external audit engagement confirmed and kickoff completed.

Budget: $23,400

Tranche 3 (Deliverable Roadmap) - Mainnet

[Deliverable 3] Mainnet Launch

Security audit findings resolved. upto scheme merged upstream, or TSC engagement fully documented if merge timing is outside our control. Bazaar and MCP server live on stellar:pubnet. All three example integrations live on mainnet: Prices API and Block Explorer API gated via the Rust crate, plus the canonical Express/TypeScript reference example. Runbook and monitoring live, targeting 99%+ uptime. Conformance report published with settled transaction hashes. Role-based developer guide published to Stellar Developer Docs.

How to measure completion: Facilitator, Bazaar, and MCP server publicly reachable on mainnet at documented URLs; Prices API and Block Explorer API each show at least one real settled mainnet transaction obtained via x402; audit report published with all findings marked resolved or explicitly accepted with rationale; conformance report published listing e2e test results and mainnet transaction hashes; monitoring dashboard accessible; professional user testing completed.

Budget: $31,200

Team

Our team operates the Soroban Block Explorer, a live production service delivered under a prior SCF Build Award, and is currently developing a Prices API under a second SCF award, on track to ship before this engagement needs to integrate it. Both are built in Rust, giving the team direct, hands-on experience with Stellar's Rust-first tooling (soroban-sdk, stellar-xdr) that this proposal builds on directly — including for the net-new Rust seller-side x402 integration this RFP requires, the first of its kind in the x402 ecosystem. Three developers will be staffed full-time for the duration of this award.