fastx402-mcp

60+ small, fast tools for your AI agent, paid per call in USDC with x402. No account, no API key, no subscription: your agent pays a fraction of a cent per successful call, on Base or Solana.

Tools include QR codes, YAML/XML/CSV/JSON conversion, Markdown to HTML, text diffs, date math and formatting, cron descriptions, time zones, color conversion, unit conversion, IP and DNS lookups, email/IBAN/ISBN validation, hashing and JWT decoding, Ethereum/Base/Solana balances, token info, transaction status, gas prices, ENS and Basename resolution, web page text, screenshots, PDF text, OCR and audio transcription. The list is read live from fastx402.tools, so new tools appear without updating this package.

Quick start

Create a new, dedicated wallet and put a few dollars of USDC in it (on Base, or on Solana). Never use your main wallet.

Claude Desktop (claude_desktop_config.json), Cursor (~/.cursor/mcp.json) and most MCP clients:

{
  "mcpServers": {
    "fastx402": {
      "command": "npx",
      "args": ["-y", "fastx402-mcp"],
      "env": {
        "FASTX402_EVM_PRIVATE_KEY": "0xYOUR_DEDICATED_WALLET_KEY",
        "FASTX402_MAX_USD_PER_DAY": "1"
      }
    }
  }
}

For Solana, set FASTX402_SOLANA_PRIVATE_KEY (base58 secret key) instead of, or next to, the EVM key.

Settings

Variable	Default	What it does
FASTX402_EVM_PRIVATE_KEY	none	Wallet that pays in USDC on Base (0x + 64 hex)
FASTX402_SOLANA_PRIVATE_KEY	none	Wallet that pays in USDC on Solana (base58, 64-byte secret key)
FASTX402_MAX_USD_PER_CALL	0.05	Refuses any single payment above this, whatever the server asks
FASTX402_MAX_USD_PER_DAY	1	Stops paying once this much was spent today (kept in ~/.fastx402-mcp/spend.json)
FASTX402_URL	https://fastx402.tools	The shop to use

Without a key the server still lists every tool, so you can look before you pay.

How paying works

1. The agent calls a tool; the server sends the request to fastx402.tools.
2. The shop answers 402 Payment Required with the exact price.
3. Your key signs a USDC authorization for that amount only, locally. The key never leaves your machine.
4. The request is repeated with the signature; the facilitator settles it on-chain (it also pays the network fee) and the answer comes back.

Failed calls (bad input 400, source down 502) are not charged. Prices are shown in every tool description.

Safety

• Use a dedicated wallet with a small balance; the limits above are a second line of defence.
• The key is only used to sign x402 USDC payments to fastx402.tools for the listed price.
• Source: this single file, index.js. Read it.

Links

• Catalog and docs: https://fastx402.tools (also /openapi.json and /llms.txt)
• Contact: [email protected]

MIT License.