Resources.
Documentation, definitions, and the curated reading list. Start with our FAQ if you're new, the glossary if you're mid-integration, or the comparison page if you're weighing pay-per-call against a traditional API.
Our docs
Start here.
FAQ
How x402 works, what it costs, how to integrate, and why pay-per-call APIs are different from traditional ones.
Read the FAQ →Glossary
x402, EIP-3009, CAIP-2, MCP, A2A, settlement, sandbox, treasury, Bazaar — in plain English.
Open the glossary →vs traditional APIs
Onboarding, auth, pricing, settlement, rate-limiting, discovery — compared row by row.
See the comparison →Protocol
The spec.
- x402.org. Specification, reference implementations, ecosystem list.
- github.com/coinbase/x402. Reference server and client code.
- RFC 7231 § 6.5.2. The original HTTP 402 status, reserved since 1997.
- EIP-3009. The "transfer with authorization" standard that makes gasless stablecoin payments possible.
Chain & asset
Base and USDC.
- base.org. Coinbase's L2, where agent commerce actually happens.
- USDC on Base. Native, not bridged. The default x402 settlement asset.
- basescan.org. Block explorer. Verify any settlement tx here.
SDKs
Building paying agents.
- Coinbase Developer Platform (CDP). Managed wallets plus x402 facilitator. The easiest path to production.
@x402/axios. Node SDK wrapping axios.@x402/fetch. Node SDK wrapping native fetch.- x402 (Python). httpx and requests support.
- viem. Lightweight Ethereum TypeScript library. What we use for key handling.
Agent frameworks
Discovery and tools.
- Model Context Protocol (MCP). How Claude and others import external tools.
- A2A (agent-to-agent) protocol. Structured inter-agent communication.
- Claude Agent Skills. Packaged capabilities your Claude agent can load.
- llms.txt. The machine-readable site index convention.
Ecosystem
Other x402 providers.
ApiToll is part of an ecosystem, not a silo. Some providers and directories worth knowing:
- x402scan.com. Directory of x402 endpoints across the ecosystem.
- x402 Bazaar. Discoverability layer run by Coinbase.
- More to come. We will add reciprocal links as the ecosystem settles.
If you're running an x402 service and want a link here, email us. We link anything we can reach and verify with a real paid call.
Data
Sources we redistribute.
- iannuttall/binlist-data. The BIN dataset behind our BIN Lookup product. CC-BY-4.0. Thank you.
Our endpoints
Machine-readable surfaces.
- /llms.txt. If you are an LLM, read this first.
- /.well-known/mcp.json. MCP server manifest.
- /.well-known/agent.json. A2A agent card.
- /health. Live status and revenue counter.