x402

• Name: x402
• URL: https://www.x402.org/
• Category: HTTP-native payments protocol / agentic payments standard / API monetization infrastructure
• Tags: ethereum-ecosystem solana-ecosystem
• Summary: x402 is the clearest HTTP-native paid-request grammar in the corpus. It standardizes a 402 Payment Required challenge/retry flow with signed payment payloads and optional facilitators. The point is the request syntax, not whichever wallet or settlement venue happens to sit underneath it.
• What it does:
  • Lets a server return 402 Payment Required with machine-readable payment requirements for a resource
  • Lets a buyer or agent sign a payment payload and retry the request with a payment header so access can be granted programmatically
  • Defines an optional facilitator role that can verify payloads, sponsor execution, and keep sellers from running chain-specific backend infrastructure themselves
  • Supports multi-network and multi-scheme execution through CAIP-style network identifiers, EVM-oriented flows, Solana support, and reference SDKs
  • Has adjacent directory/discovery work, but the durable thing here is still the paid-request handshake itself
• Key claims:
  • The official site and foundation repo describe x402 as an open standard rather than a Coinbase-only product
  • The docs explicitly frame the protocol around paid API calls, digital resources, and agent-to-agent commerce without account creation or subscription overhead
  • The protocol keeps the transport HTTP-native instead of inventing a separate proprietary session layer
  • Coinbase Developer Platform currently appears to be the most mature hosted facilitator surface, but that is an implementation layer, not the protocol itself
  • Bazaar is adjacent, but it is not the protocol. The durable thing here remains the paid-request handshake and facilitator model
• Whitepaper: Yes. The official x402 technical whitepaper was saved locally as ../../whitepapers/x402-whitepaper.pdf; current primary-source notes are in ../../whitepapers/x402-primary-sources-2026-04-27.md.
• Sources:
  • https://www.x402.org/
  • https://x402.org/x402-whitepaper.pdf
  • https://docs.cdp.coinbase.com/x402/welcome
  • https://docs.cdp.coinbase.com/x402/network-support
  • https://docs.cdp.coinbase.com/x402/core-concepts/facilitator
  • https://docs.cdp.coinbase.com/x402/bazaar
  • https://github.com/x402-foundation/x402
  • https://github.com/coinbase/x402

Internal linkages

• Closest paid-request contrast: l402
• Main account-discovery contrast: open-payments

Control surface

• x402 is thin by design. The practical leverage reappears around facilitator selection, supported settlement methods, verifier policy, wallet packaging, and which retry/signing path gets normalized for buyers.

• That is the point of keeping this note separate from vendor wrappers. The request-auth grammar is the reusable part; most operator power accumulates in the layers wrapped around it.

• Last reviewed: 2026-06-12 UTC