JWT Decoder
Decode JSON Web Tokens securely.
Decode JWTs entirely in your browser. Your tokens never leave your device.
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🔐 The JWT Revolution
JSON Web Tokens were formalized as RFC 7519 in 2015. They solved a major problem: how do you
authenticate users in stateless, distributed systems without database lookups on every request? JWTs carry
claims that can be verified cryptographically—no session store required.
🤯 Wacky Facts
- JWTs are pronounced "jots"—not "jay-double-you-tees"
- The three parts (header, payload, signature) are separated by dots, not slashes
- JWTs can be verified without contacting the issuer—that's the magic of asymmetric cryptography
- The
alg: none vulnerability let attackers forge tokens by disabling signatures entirely
- JWTs are not encrypted by default—anyone can decode the payload. Only the signature
prevents tampering!
💡 Useful Tips
- Never trust the client: Always verify JWTs on your server
- Keep payloads small: JWTs are sent with every request—don't bloat them
- Use short expiry: Access tokens should expire in minutes, not days
- Check the 'aud' claim: Ensure the token was meant for your service
- Use refresh tokens: Don't make users re-authenticate constantly
- NEVER put secrets in JWTs: The payload is base64, not encrypted!
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