JWT Decoder
Decode JWT tokens instantly. View header, payload, signature with expiration validation and security warnings. 100% client-side, no data sent to servers.
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How to Use JWT Decoder
- Copy a JWT token from your application, API response, or browser storage
- Paste the token into the "JWT Token" text area
- Tool automatically decodes in real-time (300ms debounce for performance)
- View the HEADER section showing algorithm (alg) and token type (typ)
- Review the PAYLOAD section with all claims and user data
- Check the SIGNATURE section (base64-encoded, cannot be decoded to original)
- Look for Security Information card with algorithm warnings and token status
- Check Timestamps card for issued at (iat), expires at (exp), not before (nbf)
- Green "Valid" badge means token has not expired, Red "Expired" means past expiration
- Copy individual sections using "Copy" buttons next to each section
- Click "Sample" button to load example JWT for testing and learning
- Use "Clear" button to reset and decode a different token
About JWT Decoder
The JWT Decoder is an essential tool for developers working with JSON Web Tokens (JWT) in authentication systems, APIs, and microservices architectures. JWT has become the industry standard for securely transmitting information between parties as digitally signed JSON objects. Understanding and debugging JWTs is crucial for modern web development.
JSON Web Tokens are compact, URL-safe tokens used primarily for authentication and authorization in web applications. A JWT consists of three Base64-URL encoded parts separated by dots: the header (token type and signing algorithm), the payload (claims and data), and the signature (cryptographic verification). Our decoder instantly parses all three sections, presenting them in human-readable JSON format.
Comprehensive JWT Analysis: Our tool doesn't just decode - it provides comprehensive analysis of your tokens with security insights, expiration validation, and algorithm warnings.
Key Features: - Three-Part Decoding: Separate display of header, payload, and signature components - Syntax Highlighting: Formatted JSON output with proper indentation for easy reading - Expiration Validation: Automatic checking of exp claim with visual status indicators - Timestamp Conversion: Human-readable dates for iat (issued at), exp (expiration), and nbf (not before) claims - Security Warnings: Algorithm-specific security alerts for unsafe configurations - Common Claims Detection: Automatic identification of standard JWT claims (sub, iss, aud, jti) - Copy to Clipboard: Individual copy buttons for header, payload, and signature - Real-Time Decoding: Instant parsing as you paste or modify tokens - 100% Client-Side: All processing happens in your browser - zero server communication - Sample Token: Built-in example JWT for testing and learning
Security Analysis: The tool automatically analyzes the signing algorithm and provides context-aware security warnings: - "none" Algorithm Alert: Critical warning for unsigned tokens (major security vulnerability) - HMAC (HS256/HS384/HS512): Warning about secret key security requirements - **RSA/ECDSA (RS*/ES*/PS*): Confirmation of secure asymmetric signing - Custom Algorithms**: Information display for non-standard algorithms
Token Expiration Tracking: Visual indicators clearly show token status: - Green Badge: Token is valid and not expired - Red Badge: Token has expired (exp claim is in the past) - Timestamp Display: Exact expiration date and time in local timezone - Multiple Timestamps: Shows iat (issued), nbf (not before), and exp (expires) when present
Understanding JWT Structure: The header typically contains the token type ("JWT") and signing algorithm (e.g., "HS256", "RS256"). The payload contains claims - statements about the user and additional metadata. Standard claims include sub (subject/user ID), iss (issuer), aud (audience), exp (expiration), iat (issued at), nbf (not before), and jti (JWT ID). Custom claims can contain any application-specific data. The signature is created by encoding the header and payload, then signing with a secret (HMAC) or private key (RSA/ECDSA).
Why Decode JWTs: During development, you need to verify token contents to debug authentication issues. When integrating third-party services, understanding their JWT structure is essential. Security audits require examining token claims and algorithms. API debugging often involves inspecting access and refresh tokens. Learning about JWT architecture is easier with hands-on decoding experience.
Privacy & Security: JWTs often contain sensitive user information. Our tool processes everything locally using JavaScript in your browser. No tokens are ever transmitted to external servers, logged, or stored. This makes it safe for production tokens containing real user data. However, remember that JWTs are encoded, not encrypted - the Base64 encoding can be reversed by anyone with access to the token.
Common Use Cases: Debug authentication failures by examining token claims. Verify token expiration and renewal timing. Inspect OAuth2 and OpenID Connect tokens. Analyze API access tokens and refresh tokens. Learn JWT structure for educational purposes. Validate tokens from Auth0, Firebase, AWS Cognito, and other auth providers. Troubleshoot single sign-on (SSO) implementations. Examine service-to-service authentication tokens in microservices.
Developer Workflow Integration: Copy tokens from browser DevTools (Application/Storage tab) or network requests. Paste into decoder to verify correct claims. Check expiration to debug "token expired" errors. Validate algorithm matches your server configuration. Copy decoded payload for documentation or testing. Verify custom claims are present and correctly formatted.
Common Use Cases
Frequently Asked Questions
What is a JWT token and how does it work?
JWT (JSON Web Token) is a compact, URL-safe token format for securely transmitting information between parties. It consists of three parts: Header (algorithm and type), Payload (claims/data), and Signature (cryptographic verification). The server generates JWTs after successful authentication, and clients include them in subsequent requests for authorization. The signature ensures the token hasn't been tampered with.
Is it safe to decode my JWT tokens with this tool?
Yes, completely safe. All decoding happens entirely in your browser using JavaScript. No data is sent to any server, logged, or stored. You can verify this by opening browser DevTools Network tab - no requests are made. However, remember that JWTs are encoded (Base64), not encrypted, so anyone with the token can decode it. Never share JWTs publicly.
Can this tool verify JWT signatures?
No, signature verification requires the secret key (for HMAC algorithms) or public key (for RSA/ECDSA algorithms). This tool only decodes the token and displays its contents. For signature verification, use server-side libraries like jsonwebtoken (Node.js), PyJWT (Python), or jose (various languages) with your secret/public key.
What does "Token Expired" mean?
JWTs contain an "exp" (expiration) claim - a Unix timestamp indicating when the token becomes invalid. If the current time is past this timestamp, the token is expired and should not be accepted by servers. Expired tokens typically require the user to re-authenticate or use a refresh token to obtain a new access token.
Why am I seeing a warning about the "none" algorithm?
The "none" algorithm means the JWT is not signed at all - anyone can create or modify it without detection. This is extremely dangerous and should never be used in production. It's a known security vulnerability (CVE-2015-9235). If you see this, there's likely a serious security issue with your authentication system.
What is the difference between HMAC and RSA algorithms?
HMAC (HS256, HS384, HS512) uses a shared secret key - the same key signs and verifies tokens. RSA (RS256, RS384, RS512) and ECDSA (ES256, ES384, ES512) use asymmetric keys - a private key signs, and a public key verifies. RSA/ECDSA are more secure for distributed systems where multiple services need to verify tokens but shouldn't be able to create them.
What are common JWT claims like sub, iss, and aud?
Standard claims include: sub (Subject) - user ID or identifier; iss (Issuer) - who created the token; aud (Audience) - who should accept the token; exp (Expiration) - when token expires; iat (Issued At) - when token was created; nbf (Not Before) - token not valid before this time; jti (JWT ID) - unique token identifier. Custom claims can be added for application-specific data.
Can I edit or modify a decoded JWT?
You can see the contents, but modifying a JWT requires re-signing it with the secret or private key. Simply changing values and re-encoding won't work because the signature will no longer match. The signature ensures token integrity - any modification invalidates the token. Only the party with the signing key can create valid tokens.
Why does my JWT have no expiration time?
Not all JWTs include an "exp" claim, though it's highly recommended for security. Tokens without expiration never expire automatically and remain valid indefinitely unless revoked. This is generally a security risk. Best practice is to use short-lived access tokens (15-60 minutes) with "exp" claims and longer-lived refresh tokens for obtaining new access tokens.
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