JWT Decoder

Decode and validate JSON Web Tokens (JWT)

Overview

A comprehensive online JWT (JSON Web Token) decoder and validator that helps developers inspect, validate, and debug JWTs. This free tool provides detailed token analysis, expiration checking, and signature verification, making it essential for API development and authentication debugging.

Key Benefits

  • Instant JWT parsing and validation
  • Detailed header and payload inspection
  • Expiration time verification
  • Signature validation status
  • Token structure analysis
  • Claim verification
  • Base64 decoding visualization

Primary Use Cases

  • API authentication debugging
  • Token validation and verification
  • OAuth/OpenID development
  • Session token inspection
  • Security audit compliance

Features

Main Features

  • Real-time JWT decoding
  • Automatic expiration checking
  • Header and payload parsing
  • Signature verification indication
  • Token structure validation
  • Claim inspection
  • Error detection and reporting

Technical Specifications

  • RFC 7519 compliance
  • Multiple algorithm support
  • Timestamp validation
  • JSON parsing and formatting
  • Base64URL decoding

How It Works

The JWT decoder separates and decodes the three parts of a JWT (header, payload, and signature), validates the structure, and presents the information in a readable format while checking for common issues like expiration and invalid formatting.

Steps

  1. Token structure validation
  2. Base64URL decoding of components
  3. Header algorithm verification
  4. Payload claim extraction
  5. Expiration time checking
  6. Signature presence verification
  7. Results formatting and display

Limitations

  • Cannot verify signatures without keys
  • Some custom claims may need interpretation
  • Complex encryption algorithms not supported

Examples

Basic JWT Decoding

Decoding a simple authentication token

Input:

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyfQ.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c

Output:

{
  "header": {
    "alg": "HS256",
    "typ": "JWT"
  },
  "payload": {
    "sub": "1234567890",
    "name": "John Doe",
    "iat": 1516239022
  },
  "signature": "SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c"
}

Token With Claims

Analyzing a JWT with various claims

Input:

eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwicm9sZSI6ImFkbWluIiwiZXhwIjoxNzM2MjM5MDIyfQ.8T7JKQ_wjzPwjnpO9wF3kSvF7_c5u_h_6b_dHH_Jxw4

Output:

{
  "header": {
    "alg": "HS256",
    "typ": "JWT"
  },
  "payload": {
    "sub": "1234567890",
    "role": "admin",
    "exp": 1736239022
  },
  "status": {
    "expired": false,
    "expiresIn": "2024-12-31T23:59:59Z"
  }
}

Frequently Asked Questions

What is a JWT token?

A JWT (JSON Web Token) is a compact, URL-safe means of representing claims between parties. It contains encoded JSON data and is commonly used for authentication and information exchange.

How does JWT decoding work?

JWT decoding involves splitting the token into its three parts (header, payload, and signature), Base64URL decoding each part, and parsing the resulting JSON data.

Can this tool verify JWT signatures?

This tool indicates the presence of signatures and their format but cannot verify them cryptographically as this requires the secret key or public key used to sign the token.

What information can I see in a decoded JWT?

You can see the header information (algorithm, token type), payload data (claims, user information, expiration), and the signature portion of the token.

Tips & Best Practices

Best Practices

  • Always verify token structure
  • Check expiration times
  • Validate required claims
  • Monitor algorithm usage
  • Inspect audience values
  • Verify issuer claims

Common Pitfalls

  • Using expired tokens
  • Ignoring token claims
  • Missing signature verification
  • Incorrect algorithm selection
  • Insecure token transmission

Technical Details

Supported Formats

  • Standard JWT format
  • Various signing algorithms
  • Custom claims
  • Registered claims
  • Public claims

Limitations

  • Maximum token size restrictions
  • Supported algorithm types
  • Claim name constraints

Browser Compatibility

  • RFC 7519 compliant
  • OpenID Connect compatible
  • OAuth 2.0 compatible

Security & Privacy

Data Handling

  • Client-side processing only
  • No server transmission
  • No token storage
  • Memory-only operations

Privacy Considerations

  • No data collection
  • No cookie usage
  • No tracking
  • Open source code

Resources & References

Documentation

References