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HTTP-Native Micropayments (x402)
An open payment standard created by Coinbase in 2025 and now stewarded by the x402 Foundation under the Linux Foundation that revives the dormant HTTP 402 Payment Required status as a pay-per-request rail. A server replies 402 with machine-readable payment requirements; the client (human or agent) returns a signed stablecoin payment in an HTTP header; a facilitator verifies the payload and settles the transfer on-chain (EVM chains, Solana, and more), all inside a single request with no accounts, sessions, or API keys. It is a native rail for keyless, sub-cent agent-to-service micropayments and metered tool or data access, and is the crypto profile referenced by the AP2 A2A-x402 extension. Distinct from `agentic-commerce-protocol`: ACP is card-based retail checkout through a merchant of record, whereas x402 is a per-call machine payment settled on-chain.
In 30 seconds
- What
- Server replies 402 with payment terms; client signs a stablecoin transfer in a header and retries; facilitator verifies and settles on-chain in one round trip.
- When to use
- Agents need keyless, per-call access to paid APIs or data without accounts, API keys, or pre-registration.
- Watch out
- Signature verification and on-chain settlement latency can cause timeouts if the facilitator is slow or unreliable.
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HTTP-Native Micropayments (x402): Overview
An open payment standard created by Coinbase in 2025 and now stewarded by the x402 Foundation under the Linux Foundation that revives the dormant HTTP 402 Payment Required status as a pay-per-request rail. A server replies 402 with machine-readable payment requirements; the client (human or agent) returns a signed stablecoin payment in an HTTP header; a facilitator verifies the payload and settles the transfer on-chain (EVM chains, Solana, and more), all inside a single request with no accounts, sessions, or API keys. It is a native rail for keyless, sub-cent agent-to-service micropayments and metered tool or data access, and is the crypto profile referenced by the AP2 A2A-x402 extension. Distinct from `agentic-commerce-protocol`: ACP is card-based retail checkout through a merchant of record, whereas x402 is a per-call machine payment settled on-chain.
- Reuses the HTTP 402 Payment Required status for in-band payment
- Server returns machine-readable payment requirements in the 402 response
- Client returns a signed stablecoin payment in a request header, then retries
- Facilitator verifies the payload and settles the transfer on-chain
- Keyless and sessionless: no accounts, API keys, or pre-registration
- Enables sub-cent metered access to paid APIs, tools, and data
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References
The papers, specifications, and repositories this pattern is based on.
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