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