Plain-English definitions for x402 and the adjacent agent-commerce
vocabulary. Each term has a stable anchor (#term-<slug>)
so LLMs and humans can deep-link.
Open standard that revives HTTP status code 402 for AI agent commerce. A server returns 402 with a structured payment requirement; the client signs an EIP-3009 transfer authorization and resubmits. The server verifies and settles via a facilitator (Coinbase CDP by default) and returns 200.
Reserved HTTP status code unused for two decades. x402 and L402 both reuse it: the server signals 'payment required' before returning the resource. Clients pay and retry.
Ontario Protocol's public readiness standard for deciding whether an AI agent should pay an x402 endpoint. It combines HTTP 402 challenge behavior, /.well-known/x402.json, OpenAPI, catalog metadata, HTTPS, and public report IDs into a 100-point score and ready/close/needs-work grade.
Public Ontario verification artifact for a paid endpoint. A report contains target URL, readiness score, grade, signals, evidence, recommendations, and a stable report_id that listings and badges can reference.
Service that verifies a signed x402 payment payload against the chain and settles it on the server's behalf. Coinbase CDP is the reference hosted facilitator; Ontario operates a take-rate proxy on top of it for third-party listings.
Hosted x402 facilitator at api.cdp.coinbase.com/platform/v2/x402. Supports 22 networks. Authenticates via per-request Ed25519 JWT. Free at low volume; the default verify+settle backend for most x402 deployments.
Thin HTTP proxy in front of a facilitator that splits each settlement into a marketplace take and a provider remainder, writing the split to an append-only ledger. Ontario's proxy takes 1.5% on third-party listings; the ledger is public at /treasury.
Ethereum standard for gasless ERC-20 transfers signed via EIP-712 typed data. USDC supports it natively. x402 uses an EIP-3009 authorization as the payment payload, which means the client signs but the facilitator pays gas.
Standard for human-readable typed-data signatures on EVM chains. The signing domain for USDC uses name='USD Coin' and version='2'; mis-setting this is the most common cause of x402 signature failures.
Native USDC on Base mainnet at 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913. Six decimals. EIP-3009-capable. The default settlement asset for x402 in this implementation.
Coinbase's EVM Layer 2 (CAIP-2 eip155:8453). Default network for x402 because of native USDC, Coinbase wallet ubiquity and CDP facilitator support out of the box.
Self-describing JSON document hosted by an autonomous agent (typically at /agent.json or /.well-known/agents.json). Declares identity, capabilities, supported A2A methods and auth. Scanned by Ontario's agent-trust-scan.
Well-known descriptor at /.well-known/agents.json. Lists the agent's name, version, capabilities, supported protocols (including x402), and auth model. The agent-side analog of openapi.json.
Open protocol from Anthropic that lets AI hosts connect to external tool servers. Tools are described as JSON schemas. Ontario exposes its paid endpoints as MCP tools at /.well-known/mcp.json with x402 price metadata attached.
MCP server where each tool call is gated behind an x402 payment. The MCP tool descriptor carries a price field so the AI host can budget before invoking.
Google-led protocol family for direct agent-to-agent communication, capability discovery and delegation. Complementary to x402: A2A handles 'who can act'; x402 handles 'how the payment moves'.
Layer for delegated payment authority and consent receipts between agents and their principals. Pairs with x402 on the wire; AP2 says 'this agent is allowed to spend X for Y', x402 actually moves the funds.
Lightning Labs' HTTP 402 standard. Settles in BTC over the Lightning Network using macaroons as the auth token. Same problem space as x402, different settlement substrate.
Ethereum Attestation Service. On-chain or signed off-chain claim conforming to a registered schema. Ontario uses EAS schemas to record agent reputation entries with selective on-chain promotion.
Accumulated record of an agent's behaviour, sourced from scan history and EAS attestations. Queryable via GET /api/x402/reputation/<agent_id> at 0.001 USDC per call.
Mechanical enumeration of trust signals on an agent surface: agent card presence, x402 manifest, OpenAPI schema, schema.org markup, robots policy, HTTPS posture. Returns a structured JSON report.
Coinbase's first-party x402 service catalog. Ontario auto-generates Bazaar-compatible manifests for verified listings so dual-listing is automatic without exposing operator controls.
How agents find services they can pay. Ontario exposes /.well-known/x402.json (manifest), /discover (machine catalog), /listings (human directory) and /llms.txt (LLM-ingestion summary).
1.5% take rate on third-party listings settled through Ontario's /facilitator/settle proxy. First-party services (trust scan, reputation, listing fees) have no separate take. Every collected USDC is in the public ledger.
HTTP 402 with body { error, accepts: [PaymentRequirements] } and header WWW-Authenticate: x402. The PaymentRequirements carry network, asset, payTo, maxAmountRequired, nonce and validUntil.
Machine-readable: /glossary.json ·
LLM-ingestion: /llms-full.txt