JWT Parser

What is a JWT Parser?

A JWT (JSON Web Token) parser decodes and displays the contents of JWT tokens. JWTs are compact, URL-safe tokens used for authentication and authorization in web applications. Parsing a JWT allows you to inspect its header, payload, and signature without verifying the token's cryptographic signature.

Why Use a JWT Parser?

JWT parsing is essential for debugging and understanding authentication tokens:

• Debug Authentication: Inspect JWT tokens to understand authentication issues
• View Claims: See user data, roles, permissions, and expiration times stored in tokens
• Verify Structure: Ensure tokens are properly formatted and contain expected data
• Development: Test and debug authentication flows during development
• Security Analysis: Understand what information is exposed in tokens

Common Use Cases

API Development

Debug API authentication by inspecting JWT tokens returned from authentication endpoints. Verify token structure, claims, and expiration times.

Authentication Troubleshooting

When authentication fails, parse JWT tokens to identify issues with token format, expired tokens, or missing claims.

Security Audits

Inspect JWT tokens to understand what user information is exposed. Review token claims to ensure sensitive data isn't unnecessarily included.

Learning JWTs

Understand JWT structure and format by parsing example tokens. Learn how claims are encoded and structured.

Token Validation

Before implementing token verification, parse tokens to understand their structure and ensure proper handling.

JWT Structure Explained

JWTs consist of three parts separated by dots (.):

1. Header: Contains token type and signing algorithm (e.g., HS256, RS256)
2. Payload: Contains claims (user data, expiration, issuer, etc.)
3. Signature: Cryptographic signature for token verification (not decoded by parser)

Common JWT Claims

Standard claims found in JWT payloads:

• sub (Subject): User ID or identifier
• exp (Expiration): Token expiration timestamp
• iat (Issued At): Token creation timestamp
• iss (Issuer): Token issuer identifier
• aud (Audience): Intended token recipient
• nbf (Not Before): Token validity start time

JWT Parsing Process

Our parser handles:

1. Token Input: Accepts JWT token string
2. Base64URL Decoding: Decodes header and payload (Base64URL format)
3. JSON Parsing: Converts decoded data to formatted JSON
4. Display: Shows header and payload in readable format
5. Validation: Checks token format and structure

Important Security Notes

⚠️ JWT Parsing vs Verification:

• Parsing: Decodes token to view contents (what this tool does)
• Verification: Validates signature and claims (requires secret/key)
• Never Trust Parsed Data: Always verify tokens in production code
• Signature Matters: Parsing doesn't verify token authenticity
• Expiration: Check expiration claims even when parsing

Best Practices

• Development Only: Use parsers for development and debugging, not production validation
• Verify Tokens: Always verify JWT signatures in production code
• Check Expiration: Verify token expiration before accepting tokens
• Validate Claims: Check required claims exist and have expected values
• Secure Storage: Don't log or expose full JWT tokens in production

Privacy and Security

Our JWT Parser processes all tokens entirely in your browser. No tokens are sent to our servers, ensuring complete privacy. However, remember that JWT tokens may contain sensitive user information—use responsibly.

Related Tools

If you need other developer or security tools, check out:

• Hash Generator: Generate cryptographic hashes
• Base64 Decode: Decode Base64-encoded data
• Regex Tester: Test regular expression patterns