Glossary.
Terms you'll meet when you wire an agent into ApiToll. Linkable via fragment anchors so you can deep-link from your own docs.
- x402
- An open HTTP protocol where servers charge for resources via HTTP 402 Payment Required responses carrying signed payment quotes. ApiToll is an x402 seller.
- USDC
- USD Coin — a dollar-backed stablecoin issued by Circle. ApiToll settles all payments in USDC on Base (mainnet) or Sepolia (testnet).
- Base
- Coinbase's Layer-2 Ethereum-compatible blockchain. Cheap gas, fast confirmations, USDC native. ApiToll's production network.
- Base Sepolia
- Base's testnet. Used for ApiToll sandbox endpoints. Test USDC is free from public faucets like alchemy.com/faucets/base-sepolia.
- EIP-3009
- An Ethereum standard for token transfer authorizations signed off-chain (transferWithAuthorization). Lets the payer sign a payment without paying gas — the recipient or facilitator broadcasts the transaction. ApiToll uses EIP-3009 USDC authorizations.
- Facilitator
- A service that verifies x402 payment authorizations and broadcasts the on-chain settlement. ApiToll uses Coinbase's CDP facilitator on mainnet and the community x402.org facilitator on Sepolia.
- Settlement
- The on-chain transfer of USDC from the payer's wallet to the seller's treasury. ApiToll waits for settlement before serving the response.
- CAIP-2
- A blockchain identifier standard. Base mainnet is
eip155:8453, Base Sepolia iseip155:84532. - Agent
- Software that takes autonomous actions on a user's behalf. ApiToll's primary customer. Agents have wallets and pay at request time without human intervention.
- Wallet
- An EVM-compatible address holding USDC. For agents, typically a Coinbase Smart Wallet or a CDP Server Wallet.
- Sandbox
- ApiToll's parallel testnet endpoints at /v1/sandbox/<service>/. Same response shape as production but on Base Sepolia with curated test inputs.
- Treasury
- The receiving wallet for a service's revenue. ApiToll uses one CDP Server Wallet per service for clean per-service P&L.
- Bazaar
- CDP's v2 discovery layer at agentic.market. ApiToll auto-lists production endpoints there once they settle their first mainnet payment.
- MCP
- Model Context Protocol — Anthropic's open standard for AI agents to discover and invoke tools. ApiToll publishes a manifest at /.well-known/mcp.json.
- A2A
- Agent-to-Agent — an emerging standard for inter-agent communication. ApiToll publishes an agent card at /.well-known/agent.json.
- llms.txt
- A plain-text manifest convention for LLMs to ingest. ApiToll's lives at /llms.txt.
- Receipt
- The HTTP response header (
x-payment-response) that carries the on-chain settlement transaction hash. - 402 challenge
- The HTTP response sent before payment. Carries the price, network, treasury address, and signing nonce. ApiToll's challenges are JSON-encoded.
- Counterfactual
- An EVM property: an EOA address has the same byte representation across every EVM chain. ApiToll's CDP Server Wallets work on Base mainnet and Sepolia using the same address.
- ADR
- Architecture Decision Record — a short Markdown document recording an architectural choice and its trade-off. ApiToll's ADRs are in the repo at .claude/DECISIONS.md, namespace ADR-AT-NNN.