x402 revives the dormant HTTP 402 "Payment Required" status code: a server replies with 402 plus payment terms, the client pays — usually USDC on Base, EVM chains or Solana via a signed transfer — and the request is fulfilled. Introduced by Coinbase, it has become the reference standard for charging AI agents per API request, per MCP tool call, or per byte of data.
The ecosystem below spans the whole stack: server middleware and client SDKs in every major language, hosted and self-hosted facilitators that settle payments for you, agent wallets, marketplaces like the x402 Bazaar, and hundreds of demos and starter kits. It is the largest protocol family we track.
New to x402? Start with the full protocol guide, then pick an SDK for your language from the list — sorted by GitHub stars, updated continuously.
The x402 category right now
The directory currently tracks 1,181 x402 projects. nofx leads the group with 12,595 stars, and 31 of them have cleared 100 stars, 5 of those past 1,000. Half the group sits at 1 stars or below, which is the honest shape of this space today: a short head of real adoption and a long tail of experiments.
TypeScript (46%) and Python (12%) dominate the implementation languages here, and go:github.com is the most prolific publisher with 39 x402 repositories. The recurring GitHub topics are x402, ai-agents, mcp.
291 of the 1,181 projects were updated in the last 30 days and 492 in the last 90 (42%), so activity is uneven — check the last-commit date before adopting. 118 have had no commit for over a year. The newest entrant is AgentFund, first published 2026-07.
Figures recomputed from the tracked repositories on every build.
Compare: x402 vs MPP · x402 vs Stripe · x402 vs L402
