Summary
This is a decoder for JSON Web Tokens with an x402 micropayment layer baked in. It exposes tools to inspect JWT headers, payloads, claims, and expiry timestamps without needing to paste tokens into random websites. The repository is pretty bare, just TypeScript source and config files, so you're connecting to a remote endpoint at jwt-decoder.api.klymax402.com rather than running it locally. The x402 integration means you're paying per decode operation, which is an unusual model for what's typically a free utility. Reach for this if you're already in an x402 payment flow and need JWT inspection without context switching, but for casual debugging you'd probably just use jwt.io.
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Public tool metadata for what this MCP can expose to an agent.
1 tools
security_decode_jwtUse this when you need to decode and inspect a JWT token without verifying its signature. Returns the full header, payload, and expiration status. 1. header -- algorithm (RS256, HS256, etc.) and toke1 params
Use this when you need to decode and inspect a JWT token without verifying its signature. Returns the full header, payload, and expiration status. 1. header -- algorithm (RS256, HS256, etc.) and toke
Parameters* required
tokenstringThe JWT token to decode (format: header.payload.signature)
JWT Decoder API
Decode and inspect JWT tokens without verification. Extracts header, payload, claims, expiry, and signature algorithm. Pay-per-call via x402 (USDC on Base L2) -- no API key, no signup, no rate-limit wall.
Part of the klymax402 marketplace -- 100 x402 micropayment APIs for AI agents, one wallet, USDC on Base.
Quickstart -- MCP
Add to your MCP client config (Claude Desktop, Cursor, ElizaOS, etc.):
{
"mcpServers": {
"jwt-decoder": {
"url": "https://jwt-decoder.api.klymax402.com/mcp"
}
}
}
Quickstart -- HTTP (x402)
curl -X POST "https://jwt-decoder.api.klymax402.com/api/decode" \
-H "Content-Type: application/json" \
-d '{"token":"..."}'
# -> 402 Payment Required, with an x402 payment challenge in the response body
Any x402-aware client (@x402/fetch, x402-agent-tools, ATXP) handles the 402 -> sign -> retry cycle automatically.
Tools
| Tool | Method | Path | Price | Description |
|---|---|---|---|---|
security_decode_jwt | POST | /api/decode | $0.003 | Decode a JWT token without signature verification |
security_decode_jwt
Use this when you need to decode and inspect a JWT token without verifying its signature. Returns the full header, payload, and expiration status.
Parameters
| Name | Type | Required | Description |
|---|---|---|---|
token | string | yes | The JWT token to decode (format: header.payload.signature) |
Example response:
{"header":{"alg":"RS256","typ":"JWT"},"payload":{"sub":"user123","exp":1720000000},"issuedAt":"2025-01-01T00:00:00Z","expiresAt":"2025-07-03T00:00:00Z","isExpired":false}
When to use: debugging authentication issues, inspecting token claims before API calls, or verifying token expiry. Use this BEFORE making authenticated requests to check if a token needs refreshing.
Not for: hashing data (use crypto_generate_hash), base64 encoding/decoding (use utility_encode_base64), password analysis (use security_check_password).
Example agent prompts
- "Decode and inspect a JWT token without verifying its signature"
Payment
- Protocol: x402 -- HTTP-native pay-per-call, no signup, no API key
- Network: Base L2 (
eip155:8453) - Asset: USDC
- Facilitator: Coinbase CDP (primary), PayAI (fallback)
- Also reachable via ATXP (OAuth-wrapped x402, RFC 9728 protected-resource metadata)
Part of klymax402
100 x402 micropayment APIs for AI agents -- one wallet, USDC on Base, zero signup.
- Catalog: https://klymax402.com/llms.txt
- Full API reference: https://klymax402.com/llms-full.txt
- Live stats: https://klymax402.com/stats
License
MIT
Featured
Keeps your Mac awake while Claude Code, Codex or Cursor works. Lets it sleep when they are done.
Try free for 7 days →Block distracting apps from your iPhone permanently without a 3rd party app. Free and open source.
Block now (100% free) →Notes, actions and memory. Without a meeting bot. First month 100% off.
Download for free →belt cli automatically finds the best tools and skills for your agent. image, video, music, tts...
one prompt install →Free an open-source skills that make AI coding agents easier to understand, verify, and control.
Download for free →Connect your Claude agent to live crypto prices and trading routes via 1inch
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