x402 SDKs & Tooling

Everything you need to pay for, or charge for, HTTP APIs in stablecoin over x402. All packages are non-custodial and open source.

@cryptoapis-io/x402-buyer-sdk (github) — the buyer capability as an npm SDK for apps and agent frameworks: register a wallet, authorize, sign locally, retry.
@cryptoapis-io/mcp-x402-pay (github) — an MCP server exposing an x402_pay tool: fetch a URL and, on a 402, pay it automatically and return the paid response. Works in any MCP-capable agent.
x402 agent plugin — a Claude Code plugin bundling the buyer tool and a merchant-integration skill. Install with /plugin marketplace add CryptoAPIs-io/cryptoapis-x402-agent-plugin.

@cryptoapis-io/x402-merchant-sdk (github) — zero-dependency middleware for Express / Hono / Next.js that adds a per-request paywall and runs the verify/settle round-trip.

@cryptoapis-io/offline-signer (github) — offline, local transaction and EIP-712 signing across EVM, UTXO, Tron, XRP, Kaspa and Solana. Pairs with the buyer flow so your key signs locally, never over the wire.

x402 is an open standard — see x402.org. Crypto APIs implements both sides so you can adopt it without running your own facilitator.

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