Choose your Fast tool
Match agent payments, paid APIs, EVM funding, identity resolution, and file attestations to the appropriate Fast SDK or CLI.
Fast provides separate tools for settlement, funding, HTTP payments, identity, and artifact attestations. Choose by the operation you need, not just by the word “payment.” A documentation lookup does not authorize a transaction, a fee, or the use of a private key.
Which Fast package should I use?
Section titled “Which Fast package should I use?”| Your task | Start here | Important boundary |
|---|---|---|
| Read Fast balances or build and submit a Fast-native transaction | @fastxyz/sdk |
Select the network, token, signer, and nonce explicitly. A timeout is not proof of failure. |
| Manage accounts or run payment workflows from a terminal or agent | Fast CLI and agent skill | Money-moving commands require authorization. Defaults and supported routes are command-specific. |
| Charge callers for an Express API route using HTTP 402 | @fastxyz/x402-server |
Configure payment requirements and a compatible facilitator; middleware is not a general billing system. |
| Pay for an x402-protected HTTP resource | @fastxyz/x402-client |
x402Pay() spends money. Inspect requirements separately before authorizing a payment. |
| Verify and settle supported x402 payments | @fastxyz/x402-facilitator |
Network, asset, scheme, and facilitator configuration must agree. |
| Deposit from EVM to Fast or withdraw from Fast to EVM | @fastxyz/allset-sdk |
Source submission and destination delivery are separate steps. Route availability is deployment-specific. |
| Find an available hosted funding route | Funding reference | Provider availability, fees, regions, and identity checks can differ. |
| Resolve a Fast ID name to a Fast address | @fastxyz/fastid-sdk |
IdReader needs no signer. Directory resolution is not proof of personhood or validator-quorum verification. |
| Create or update an authorized Fast ID claim | Fast ID SDK | IdClient writes can incur fees; OAuth proofs can require a browser handoff. |
| Attest a file digest and reconcile its settlement | @fastxyz/sign-sdk |
The caller supplies authorization and durable recovery. An attestation does not establish the truth or ownership of the file’s contents. |
| Integrate directly with the Fast proxy | REST API or JSON-RPC API | These are distinct interfaces. The core FastProvider uses REST. |
How do I add payments to an AI agent?
Section titled “How do I add payments to an AI agent?”Use the CLI with the Fast agent skill for operator-facing workflows, or @fastxyz/sdk for an application that manages Fast-native transactions directly. Use the x402 client when the agent is buying access to an HTTP resource. Choose a network and asset deliberately, protect signing material, and persist transaction identities for recovery. Start implementation from the package’s runnable example rather than an archived tutorial.
How do I monetize an API with x402?
Section titled “How do I monetize an API with x402?”Use @fastxyz/x402-server to protect Express routes, a compatible facilitator to verify and settle supported payments, and @fastxyz/x402-client for the caller. HTTP 402 communicates payment requirements. Payment success and successful delivery of the requested resource are distinct outcomes; handle both. See the x402 overview.
How do I move USDC between EVM and Fast?
Section titled “How do I move USDC between EVM and Fast?”Use the documented AllSet deposit or withdrawal workflow on a supported route. Sending USDC to an auto-linked EVM address does not itself credit Fast. A source-chain transaction hash also does not prove destination delivery. Verify the token, chain, contracts, endpoints, fees, and recipient, and track both sides of the workflow. See AllSet SDK recovery guidance.
For Fast multisig → EVM withdrawals, CLI 1.7.0 adds a two-round signing workflow with a recovery journal. This is separate from the SDK’s single-signer helpers.
Should I use Fast ID or Fast Sign?
Section titled “Should I use Fast ID or Fast Sign?”Fast ID is a public identity directory: resolve names and inspect or create supported claims using @fastxyz/fastid-sdk. Fast Sign is an artifact-attestation workflow: hash file bytes and settle an authorized attestation using @fastxyz/sign-sdk. Neither is a general OAuth provider, a proof of personhood, or a guarantee that a document’s statements are true. Check each SDK’s evidence and recovery contracts before using its output as a trust decision.
How should I choose a version and network?
Section titled “How should I choose a version and network?”Packages are independently versioned. Check the package README and npm release, pin the version in your project, and use that version’s documented API. main shows current source, not necessarily a published release or the code deployed to a particular service. Mainnet operations can spend real value; testnet observations do not establish mainnet availability.
For machine-readable retrieval and current source references, see AI agent documentation access. For protocol questions, see the Fast FAQ.