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FastX402 Lab JWT Decoder
x402
FastX402 Lab JWT Decoder is a paid API for AI agents from fastx402.tools, paid per call via x402, $0.001/call, status unknown (last checked 2026-10-17).
Decodes a JWT's header and payload, reporting algorithm, issue/expiry times, expiration status, and seconds until expiry — without verifying the signature.
Price / call$0.001
Success—
StatusUnknown
How this service works
146 pay-per-call tools for AI agents, from $0.001 per request in USDC on Base or Solana with x402. No account, no API key.
Output
Returns a JSON object containing the decoded JWT header (alg, typ), the decoded payload (sub, iat, exp, plus any other claims), the algorithm string, human-readable issued_at and expires_at timestamps in ISO 8601, an expired boolean, whether a signature is present, and the number of seconds until expiry (negative if already expired).
Example use cases
Debugging expired auth token
“I'm getting a 401 error and I think my JWT might be expired — can you decode this token and tell me when it expires and whether it's still valid? eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJhZ2VudC00MiIsImlhdCI6MTc5MDAwMDAwMCwiZXhwIjoxNzkwMDAzNjAwfQ.signature”
Checking JWT algorithm in use
“What signing algorithm is this JWT using? eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJ1c2VyLTEiLCJpYXQiOjE3OTAwMDAwMDAsImV4cCI6MTc5MDAwMzYwMH0.sig — I need to know if it's HS256 or RS256 before I update the auth middleware.”
Inspecting token lifetime during CI test
“During our integration test, decode this JWT and confirm it won't expire in the next 10 minutes: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiJ0ZXN0LXVzZXIiLCJpYXQiOjE3OTAwMDAwMDAsImV4cCI6MTc5MDA2MDAwMH0.testsig — use 1790000000 as the current time for a reproducible result.”
Technical details
Endpoint
GEThttps://fastx402.tools/jwt-decode?utm_source=zero.xyzWhen to prefer
Choose this endpoint when you need to quickly inspect JWT claims, algorithm, or expiration status during debugging or automation — especially when signature verification is unnecessary or the secret/key is unavailable. It is ideal for lightweight token inspection in CI pipelines, agent auth flows, or log analysis. Prefer a full JWT verification library when you actually need cryptographic signature validation.
Side effects
- Malformed or non-JWT string causes a parse error response
- Missing required 'token' query parameter returns a validation error
- Token with no expiry claim (no 'exp') may return null or zero for expiry-related fields
- Network or payment failure returns a 402 or 5xx response
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| inputrequired | object | |
| output | object |
Output
Schema · Response
{
"type": "json",
"example": {
"header": {
"alg": "HS256",
"typ": "JWT"
},
"expired": false,
"payload": {
"exp": 1790003600,
"iat": 1790000000,
"sub": "agent-42"
},
"algorithm": "HS256",
"issued_at": "2026-09-21T14:13:20Z",
"expires_at": "2026-09-21T15:13:20Z",
"signature_present": true,
"seconds_until_expiry": 1800
}
}Tags
x402
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