Glossary

x402 An HTTP-friendly standard for per-request payments. Calls either include valid proof of payment or receive 402 Payment Required.

Faremeter Middleware that enforces x402 on Solana. Verifies payment before a request is forwarded to your original API.

MCP (Model Context Protocol) A protocol that lets AI agents discover and call “tools” (functions/APIs) in a consistent way. xPay auto-publishes your endpoints as MCP tools.

Agent Software that plans, decides, and calls APIs autonomously using AI. Agents prefer protocols (like MCP and x402) over dashboards and keys.

SPL Token Token standard on Solana. USDC is an SPL token frequently used for stable pricing.

Mint Address The on-chain address identifying an SPL token. You can use any SPL token by its mint address.

Proxy URL The xPay-wrapped endpoint (e.g., https://api.usexpay.xyz/:username/:endpointName) that enforces x402 payments and forwards to your original API.

Sample Body / Sample Response Example request/response payloads you provide when registering an endpoint. Used to improve docs and auto-generate MCP tool schemas, as well as inform agents about the expected payload.