# Utter

> You utter a sentence. You get a paid API that AI agents pay for per call in USDC on Arc.

## Docs

- [Utter](https://docs.utter.technology/index.md): You utter a sentence. You get a paid API that AI agents pay for per call in USDC.
- [How it works](https://docs.utter.technology/start/how-it-works.md): The full loop from a sentence to a paid API that agents pay for per call.
- [Is Utter for me?](https://docs.utter.technology/start/is-utter-for-me.md): One question sorts you: do you want to sell an API or buy one? Pick a path.
- [Quickstart: create a paid API](https://docs.utter.technology/start/quickstart-create.md): Utter a sentence and get a live endpoint agents pay for, in about two minutes.
- [Quickstart: pay for an API](https://docs.utter.technology/start/quickstart-pay.md): Point an agent at an endpoint and have it discover and pay per call in USDC.
- [Creating a paid API](https://docs.utter.technology/create/overview.md): Describe an endpoint in one sentence and get a live URL that agents pay for per call, in about two minutes.
- [The studio and the build stream](https://docs.utter.technology/create/studio-and-build.md): Compose a sentence, press utter, and watch six stages take it from generated code to a live endpoint.
- [Pricing and bonds](https://docs.utter.technology/create/pricing-and-bonds.md): Set a flat or metered price, understand the buyer-signed cap and the 70/30 split, and post the bond that backs your endpoint.
- [Iterate on an endpoint](https://docs.utter.technology/create/iterate.md): Refine your prompt and re-utter. Every change is a fresh generation that has to pass the gates again.
- [Earnings and withdraw](https://docs.utter.technology/create/earnings-and-withdraw.md): Where your 70% of every call accrues, how the dashboard reads it from on-chain legs, and how to withdraw.
- [Reputation and strikes](https://docs.utter.technology/create/reputation-and-strikes.md): How the scorer probes your endpoint, why a bad buyer input never strikes you, and what five consecutive failures do.
- [Paying for APIs](https://docs.utter.technology/pay/overview.md): How an AI agent deposits USDC once, then discovers and pays for endpoints per call with no keys and no humans.
- [Discovering endpoints](https://docs.utter.technology/pay/discover.md): Read the public marketplace index, then read the agent card. The card is the single source of everything an agent needs to pay.
- [The buyer SDK (CLI)](https://docs.utter.technology/pay/buyer-sdk.md): The pay CLI: fund the escrow once and fire real paid calls to a live endpoint, with a settlement tx and an ArcScan link per call.
- [The MCP server](https://docs.utter.technology/pay/mcp.md): Expose discovered Utter endpoints as tools an agent calls from Claude Desktop or Cursor, with a safe in-process demo mode by default.
- [Deposits and spend caps](https://docs.utter.technology/pay/deposits-and-caps.md): How the escrow balance funds every call, how the buyer bounds what it signs, and how a lost response is recovered without paying twice.
- [The escrow response gate](https://docs.utter.technology/concepts/escrow-response-gate.md): The core primitive: an agent pays only after the response passes validation.
- [The x402 utter-escrow scheme](https://docs.utter.technology/concepts/x402-scheme.md): How Utter extends x402 with an escrow scheme that locks funds, meters, and gates on the response.
- [Metering and response classification](https://docs.utter.technology/concepts/metering-and-classification.md): How the final price is computed against the response and how a response is graded success, declared error, or malfunction.
- [Exactly-once settlement](https://docs.utter.technology/concepts/exactly-once.md): The payment nonce is the idempotency key, and three layers make sure a retry never double charges and never re-signs.
- [Wallets and SIWE sign-in](https://docs.utter.technology/concepts/wallet-and-siwe.md): How a creator signs in with their wallet using SIWE, how API keys work, and where a buyer's on-chain funds live.
- [On-chain identity (ERC-8004)](https://docs.utter.technology/concepts/erc8004-identity.md): Each resource gets an on-chain ERC-8004 identity: a minted agentId that the registry, the agent card, and the reputation score all agree on.
- [The agent card (A2A)](https://docs.utter.technology/concepts/agent-card.md): The A2A agent card is the machine-readable contract an agent reads to discover, verify, and pay an endpoint.
- [The gVisor sandbox](https://docs.utter.technology/concepts/sandbox.md): Untrusted generated code runs only under gVisor, with a hardened run-spec, hard caps, and a trusted sidecar in front that owns the money path.
- [The static gate and egress proxy](https://docs.utter.technology/concepts/egress-and-static-gate.md): Two controls keep generated code safe: a pre-build static scan that rejects bad bundles, and a deny-by-default data proxy that is the only way out.
- [Arc: USDC as gas and settlement](https://docs.utter.technology/concepts/arc.md): Why Utter is built on Arc, Circle's stablecoin L1, where USDC is both the gas token and the settlement asset.
- [Call endpoint](https://docs.utter.technology/reference/call-endpoint.md): The POST /call payment gate every deployed Utter resource exposes, its 402 quote, and its outcomes.
- [Marketplace API](https://docs.utter.technology/reference/marketplace-api.md): The Hono JSON service agents read to discover resources and fetch validated agent cards.
- [Facilitator API](https://docs.utter.technology/reference/facilitator-api.md): The Hono service that runs the escrow money path: verify, release, settle, and results.
- [Contracts](https://docs.utter.technology/reference/contracts.md): The Solidity contracts behind the escrow money path, resource registry, staking, and splitting.
- [Addresses and chain](https://docs.utter.technology/reference/addresses.md): Arc Testnet network parameters and every pinned contract address Utter uses.
- [Buyer SDK](https://docs.utter.technology/reference/buyer-sdk.md): The @utter/buyer-sdk pay CLI, the MCP server, and the programmatic client agents use to pay per call.
- [Agent card schema](https://docs.utter.technology/reference/agent-card-schema.md): The A2A agent card every Utter resource serves, with its full field reference.
- [Environment](https://docs.utter.technology/reference/environment.md): The environment variables Utter reads, grouped by area, from .env.example.
- [Glossary](https://docs.utter.technology/reference/glossary.md): Every Utter term in one place, alphabetized, with links to the concept pages.
- [Architecture](https://docs.utter.technology/operator/architecture.md): The monorepo map, the services that carry the loop, and the network topology that makes isolation real.
- [The deploy pipeline](https://docs.utter.technology/operator/deploy-pipeline.md): The ordered steps a generated bundle runs through, from an authenticated request to a live paid endpoint.
- [Provisioning a host](https://docs.utter.technology/operator/provisioning.md): The gVisor host, wildcard TLS, durability, and the systemd deployer that make real isolation possible.
- [Self-hosting the stack](https://docs.utter.technology/operator/self-hosting.md): The practical shape of running Utter yourself: install, env, test, compose up, and the host deployer.