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fastapi.online JWT Decode
x402
fastapi.online JWT Decode is a paid API for AI agents from api.fastapi.online, paid per call via x402, $0.0005/call, status unknown (last checked 2026-09-14).
Decodes a JWT token and returns its header, payload, and signature components without verification
Price / call$0.0005
Success—
StatusUnknown
How this service works
Chat, embeddings, OCR, speech-to-text, image editing, image understanding (captioning/Q&A), text-to-speech, translation, writing tools, classification tools, developer tools, local utilities, format/checksum validators, encoding & crypto utilities, date/time calculators, geo/coordinate math, math & finance calculators, novelty tools, and business/social writing generators — 179 endpoints in all, across multiple specialized self-hosted models. Pay per call with crypto — no signup — or get an API key.
Output
Returns the decoded JWT broken into its three components: the header object (containing algorithm and token type), the payload object (containing all claims such as sub, iat, exp, roles, and any custom claims), and the signature string — all without performing cryptographic signature verification.
Example use cases
Inspect auth token claims
“I have this JWT from our auth system and I need to see what claims are inside it — can you decode it for me? Here's the token: eyJhbGciOiJSUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VySWQiOiJhYmMxMjMiLCJyb2xlIjoiYWRtaW4iLCJleHAiOjE3MDA1MDAwMDB9.signature”
Debug expired token payload
“I'm getting auth errors in my app and I want to check if this JWT is expired — can you decode it and show me the exp and iat fields? Token: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpYXQiOjE2MDAwMDAwMDAsImV4cCI6MTYwMDAwMTAwMH0.abc123”
Audit third-party token structure
“We received a JWT from a third-party service and I need to understand its structure — what algorithm is it using in the header and what data is in the payload? Here's the token: eyJhbGciOiJFUzI1NiIsInR5cCI6IkpXVCIsImtpZCI6ImtleS0xIn0.eyJzdWIiOiJ1c2VyXzQ1NiIsInNjb3BlcyI6WyJyZWFkIiwid3JpdGUiXX0.signature_here”
Technical details
Endpoint
POSThttps://api.fastapi.online/jwt-decodeWhen to prefer
Use this endpoint when you need to quickly inspect or debug the contents of a JWT token without needing cryptographic signature verification. It is ideal for development and debugging workflows where you want to read claims, check expiry, or audit token structure. Prefer this over manual base64 decoding for convenience in agent pipelines.
Side effects
- Malformed or non-JWT string returns a parsing error
- Token exceeding 8000 characters is rejected
- Empty token string is rejected by input validation
- Network or payment failure (402) if USDC payment is not provided
- Signature is NOT verified — this endpoint only decodes, does not authenticate
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| token | string |
Tags
x402
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