Introduction

Vellar is an x402 facilitator with Bazaar discovery — a hosted service that verifies and settles HTTP 402 payments on Stellar, paired with a catalog so AI agents can find and pay for resources without hardcoded URLs.

By the end of this page you will understand what Vellar is, what problem it solves, and which part of the docs to read next based on what you are building.

What Vellar is

Vellar is a programmable payment platform for Stellar that lets people and AI agents discover, pay for, and be governed on services, with the rules enforced by consensus rather than by your application code. The x402 payment layer Vellar runs — a live verify/settle facilitator with Bazaar discovery — is live on Stellar testnet today, reachable straight from a terminal via vellar-cli or from an AI agent via the MCP payer. Every settled payment auto-catalogs its resource so agents can find what to pay for, and a payment can be governed on-chain by spending-limit and verified-only policies. The facilitator raises its fee ceiling specifically to accept those policy-governed payments, which the reference facilitator rejects.

The components

x402 facilitator

A live verify/settle facilitator that re-simulates each payment on-chain, settles the SEP-41 transfer, and sponsors the network fee. People and agents pay for HTTP-402 resources while holding no XLM themselves, and a seller points at the facilitator once and charges per request without touching Soroban RPC, auth entries, or fee handling.

Bazaar discovery

Every settled payment auto-catalogs its resource, so a service shows up in the catalog just by getting paid, with no separate registration step. An agent needs this because it is otherwise hardcoded with URLs: with Bazaar it searches by keyword and each result carries the exact asset, amount, and payTo it needs to pay. The facilitator also ships an MCP stdio server exposing the catalog as agent tools, so an AI agent can search for payable resources without hardcoded URLs.

CLI and MCP payer

vellar-cli discovers, quotes, pays for, and inspects x402 resources from a terminal — no wallet setup, no browser. vellar-mcp-x402-payer gives an AI agent the same capability as an MCP stdio server, holding exactly one key with process-level and on-chain budget layers so a spending mistake or a compromised agent still can't exceed what you authorized.

Agent spending controls

A spending-limit policy caps how much an agent can move per fixed window; a verified-only policy restricts it to contracts whose source has been reproducibly verified — provenance, not an audit. Both are enforced by Stellar consensus rather than by your code, so the limits bind even a fully compromised agent that bypasses your application entirely. See Policies.

Passkey smart wallet — optional

For apps that want passkey-based smart accounts: WebAuthn onboarding (Face ID / Touch ID) backed by Soroban smart-contract accounts, with no seed phrase and fee-sponsored submission. This is the account layer buyers and agents pay from, but you don't need it to pay for a Bazaar resource from a script or an agent — a plain funded keypair works for that. See Wallet API Reference if you're building a consumer wallet.

Who this is for

Developers adding payments to an existing endpoint who want to charge per request without Stellar plumbing. Point your resource server's facilitator client at the hosted URL and your API gains x402 payments; declare the bazaar discovery extension on a route and it is cataloged automatically after its first settled payment.

Teams building AI agents that spend money who need programmable, on-chain security instead of client-side checks that can be bypassed. An agent holds a scoped key bounded by a spending-limit policy the chain enforces — give your agent a budget, not your keys.

Developers building user-facing apps on Stellar who want login and a wallet without becoming wallet-infrastructure experts. Passkey onboarding replaces seed phrases, deployment and fees are sponsored, and the SDK exposes one object with create, connect, and pay.

Status

⚠️ Testnet by default; mainnet exists. Every tool here defaults to the testnet facilitator, and every example in these docs spends test USDC. A separate mainnet deployment is live and moves real funds.

One pre-mainnet gate is still open: the spending-limit policy contract has not had a mainnet security audit. The facilitator review is complete; the policy contract is separate work.

APIs may change before 1.0.

Where to start

I want to...	Start here
Accept payments on my API	Charge for an endpoint
Have an agent pay for resources	Pay for a resource and the CLI
Run my own facilitator	Run the facilitator
Give my agent a spending budget	Policies
Understand how it works	How it works
Build a passkey wallet for my users	Wallet API Reference