captcha-mcp
PoW CAPTCHA verification for MCP clients. Exposes generate_challenge and verify_solution tools — stateless proof-of-work that agents can embed in auth flows. L402 Lightning skip tier available for trusted clients. No API key required for PoW path.
How to connect
https://captcha-mcp--zekebuilds.run.tools
tools/list returns the expected tools before relying on them in production.Tools
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challengeRequest a fresh PoW challenge from the PowForge captcha service. Returns {id, salt, difficulty, signature, instructions}. The agent must find a nonce such that SHA-256(salt + nonce) has at least `difficulty` leading zero bits, then call the verify tool. Free tier — no payment required.
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verifyVerify a PoW solution. Input: {salt, nonce, id, signature, algo?, difficulty?} from a prior challenge call plus the nonce the agent computed. Returns a 5-minute HMAC-signed token on success, or {valid: false, reason} on failure. Tokens can be re-verified server-side via POST /api/token/verify.
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statusReturn PowForge captcha server health, lifetime stats (pow_solves, ln_skips, challenges_issued), and L402 endpoint metadata (scope, price_sats, paid endpoint URL). Use this to discover the Lightning skip price before paying, or as a liveness check.