About JWT Parser

Use JWT Parser to Decode JSON Web Tokens. The tool runs in your browser for fast results and keeps your data local.

How to Use

  1. 1. Add your input or data.
  2. 2. Adjust options if needed.
  3. 3. Review the result and copy it.

What is JWT?

JWT (JSON Web Token) is a compact, URL-safe token format for securely transmitting information between parties as a JSON object. A JWT consists of three Base64-encoded parts separated by dots: header (algorithm and token type), payload (claims/data), and signature (verification). JWTs are commonly used for authentication and authorization—after login, the server issues a JWT that the client includes in subsequent requests. The signature ensures the token has not been tampered with. JWT parsing decodes the header and payload to inspect claims like user ID, expiration time (exp), and issued time (iat). Understanding JWT structure is essential for API security and debugging authentication issues.

Common Use Cases

JWT parsing is essential for API development and security debugging. Backend developers debug authentication issues by inspecting JWT claims. Frontend developers verify token contents and expiration times. Security researchers analyze JWT structure for vulnerabilities. API integrators troubleshoot third-party authentication tokens. DevOps engineers verify JWT configuration in microservices. Mobile developers debug token refresh logic. Penetration testers examine JWT security implementations.

  • Debugging authentication and authorization issues
  • Verifying token claims and expiration
  • Security analysis for vulnerabilities
  • Troubleshooting third-party auth integrations
  • Microservices JWT configuration verification
  • Mobile app token refresh debugging
  • Penetration testing JWT implementations
  • Understanding token structure and contents

Best Practices & Tips

Always verify JWT signatures on the server—parsing alone does not validate authenticity. Check expiration (exp) and not-before (nbf) claims to prevent token reuse. Use strong signing algorithms (RS256, ES256) instead of HS256 for public APIs. Store JWTs securely—avoid localStorage for sensitive tokens, use httpOnly cookies. Implement token refresh to minimize exposure time. Include minimal data in JWT payload—it is not encrypted, only signed. Validate issuer (iss) and audience (aud) claims to prevent token misuse. Use short expiration times (15 minutes) with refresh tokens for security.

  • Always verify signatures on server, not just decode
  • Check exp and nbf claims to prevent reuse
  • Use RS256/ES256 for public APIs, not HS256
  • Store in httpOnly cookies, not localStorage
  • Implement token refresh for security
  • Include minimal data—JWT is signed, not encrypted
  • Validate iss and aud claims to prevent misuse
  • Use short expiration (15min) with refresh tokens

Troubleshooting Common Issues

If JWT parsing fails, verify the token has three parts separated by dots. If Base64 decoding fails, the token may be corrupted or truncated. If signature verification fails, check the signing key and algorithm match. If token is expired, check the exp claim and implement token refresh. If claims are missing, verify the token was issued correctly. If algorithm is "none", this is a security vulnerability—reject such tokens. If token is too large, reduce payload size or use reference tokens. If special characters cause issues, ensure proper URL-safe Base64 encoding.

  • Token missing three dot-separated parts
  • Base64 decoding failing from corruption
  • Signature verification failing from wrong key
  • Expired tokens with old exp claim
  • Missing expected claims in payload
  • Algorithm "none" security vulnerability
  • Token too large for headers or URLs
  • Special characters breaking URL-safe encoding

Frequently Asked Questions

Is JWT Parser free to use?

Yes. JWT Parser is free and works directly in your browser.

Does JWT Parser upload my data?

No. Most processing happens locally. Any network requests are clearly indicated.

What formats does JWT Parser support?

JWT Parser supports the common formats described on the page. Convert uncommon formats before pasting.

How should I share results from JWT Parser?

Copy the output and review any sensitive data before sharing or publishing.