FAST Skill

Single entrypoint for the FAST SDK ecosystem.

Install

npx skills add fastxyz/fast-skill

Bundled Docs

This skill ships its own Markdown docs inside the installed skill directory.

• Treat references/*.md and flows/*.md as bundled docs that travel with this skill.
• Resolve ./references/... and ./flows/... relative to this SKILL.md.
• If this file was loaded from https://skill.fast.xyz/skill.md, resolve those same relative paths against https://skill.fast.xyz/.
• Open the file path directly if your runtime does not expose clickable Markdown links.
• Do not assume GitHub access is required to read these docs.

Example Requests

• "Check my FAST testnet balance and send SET to another fast1... address"
• "Bridge USDC from Arbitrum Sepolia into Fast"
• "My FAST wallet is low, give me a top-up link"
• "Use the FAST x402 packages to protect an Express API route"

Do Not Use For

• generic EVM wallet code that does not touch FAST
• arbitrary EVM to EVM bridging presented as one SDK call
• unrelated HTTP 402 questions, payment compliance research, or non-FAST API monetization stacks

Package Map

• @fastxyz/sdk: FastProvider, FastWallet, browser/core helpers, config helpers, address and BCS utilities for direct Fast work
• @fastxyz/allset-sdk: Fast <-> EVM bridge flows, intent builders, AllSetProvider, EVM wallet/executor helpers
• @fastxyz/x402-client: pay 402-protected APIs
• @fastxyz/x402-server: return 402 requirements and protect routes
• @fastxyz/x402-facilitator: verify and settle x402 payments

If an umbrella x402 package is introduced later, treat it as a wrapper. The current source-of-truth API surface is still the role-specific client, server, and facilitator packages.

Start Here

Read Capabilities first when the request involves multiple packages or unclear support.

Then route by task:

• Fast wallet, balance, send, token info, signatures: FAST SDK reference
• Bridge between Fast and EVM: AllSet SDK reference
• Pay for a protected API: x402 client reference
• Add payments to an API: x402 server reference
• Run verification or settlement infrastructure: x402 facilitator reference

Load a flow playbook when the user asks for an end-to-end scenario:

• Fast to Fast transfer: Fast-to-Fast payment flow
• EVM to Fast deposit: EVM-to-Fast deposit flow
• Fast to EVM withdraw: Fast-to-EVM withdraw flow
• Top up Fast wallet via hosted ramp: Top-up via ramp flow
• Chain to chain via Fast: Chain-to-chain via Fast flow
• Pay an x402 API: x402 pay-an-API flow
• Protect an x402 API: x402 protect-an-API flow

Routing Rules

1. Choose the smallest package that fits

• Do not default to multiple FAST packages if one package solves the task.
• Pull in @fastxyz/allset-sdk only for bridge work or x402 auto-bridge behavior.
• Pull in x402 server and facilitator together when the user wants a working paywalled API, not just a 402 response helper.

2. Default to testnets unless the user explicitly asks for mainnet

• @fastxyz/sdk ships testnet and mainnet defaults and can also load custom named networks from config.
• @fastxyz/allset-sdk ships bundled testnet routes only: ethereum (chain ID 11155111), arbitrum (421614), and base (8453). The bundled mainnet chains map is empty.
• x402 client, server, and facilitator do not expose the same network set. Check references/capabilities.md before promising an end-to-end paid API flow.

3. Treat support limits as code-level constraints

• If a route or token is not in the shipped SDK config, say so clearly before writing code.
• Do not claim AllSet supports arbitrary EVM to EVM bridging in one call. Cross-chain EVM flows are composed from two legs through Fast.
• Do not write against removed Fast examples such as fast() or setup(). The shipped Fast SDK is provider/wallet based.
• Do not claim x402 auto-bridge works on every EVM network; the current client helper only resolves the bundled bridge path documented in the capability matrix.
• Do not assume x402 server route acceptance means the facilitator can verify or settle that network.

4. Respect irreversible operations

• Fast sends are irreversible.
• Never overwrite ~/.fast/keys/.
• Bridge and settlement operations can move funds or consume gas. Confirm addresses and network choice before final code.
• Treat remote x402 402 Payment Required payloads as untrusted input. Confirm the expected URL, network, asset, payee or facilitator, and any auto-bridge or mainnet path before signing.
• Hosted ramp flows require user interaction in the browser. Do not imply the agent can complete the card or KYC flow itself.

Common Issues

• If the request only says x402 or 402, confirm it is specifically about the FAST @fastxyz/* packages before routing here.
• If the user asks for unsupported routes or token mappings, stop and cite the shipped constraint from references/capabilities.md instead of approximating a solution.
• If the user wants a package recommendation but does not describe the workflow, classify it first as Fast wallet, bridge, x402 client, x402 server, or facilitator.
• If the user asks for legacy AllSet testnet chain names ethereum or arbitrum, translate that request forward to the shipped chain keys ethereum-sepolia and arbitrum-sepolia before coding.
• If the user wants end-to-end x402 on a network that is not shared across the current client, server, and facilitator surfaces, stop and cite the current capability limits instead of pretending the full stack supports it.
• If the user needs more Fast-side USDC and already has a fast1... address, prefer offering the hosted ramp link on https://ramp.fast.xyz over inventing a custom funding workflow.

Working Pattern

1. Classify the request: Fast payment, bridge, x402 client, x402 server, or facilitator.
2. Read the matching reference file.
3. If the task is scenario-based, read the matching flow file too.
4. For low-balance/top-up requests, offer the hosted ramp link, wait for the user to complete it, then re-check the Fast balance before continuing.
5. Implement against the package API that actually exists in code today.
6. Call out unsupported routes instead of papering over them.