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JWT Decoder
Decode and inspect JSON Web Tokens
About JWTs
- • JWTs consist of three parts: Header, Payload, Signature
- • Header and Payload are Base64Url encoded
- • Signature verifies the token hasn't been tampered with
- • Never store sensitive data in JWTs - they're not encrypted!
What is JWT Decoder?
A JWT (JSON Web Token) decoder parses the three Base64URL-encoded segments of a JWT -- header, payload, and signature -- and displays their contents in readable JSON. The header specifies the algorithm, the payload contains claims (user data, expiration, permissions), and the signature verifies integrity.
How to use this calculator
- 1Paste your JWT token — the long string separated by two periods — into the input field.
- 2Review the decoded header to confirm the algorithm used for signing.
- 3Check the payload for claims: user ID, email, roles, expiration (exp), and issued-at (iat).
- 4Verify the expiration timestamp against the current time to diagnose authentication failures.
- 5Note: this tool decodes the payload but does NOT verify the signature — use your backend auth library for that.
Why this matters for founders
JWTs are the dominant authentication token format in modern web applications. Being able to quickly inspect a token's contents is essential for debugging auth flows, verifying claims, checking expiration times, and diagnosing permission issues.
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