🚀 Quick Start Guide

1. Paste a JWT token in the left editor to decode it instantly
2. View decoded header, payload, and signature separately
3. Verify token signature with the secret key
4. Generate new tokens with custom claims
5. Check token expiration and validation status

🔍 Understanding JWT Structure

Header: Contains token type and signing algorithm

Payload: Contains claims (data) about the entity

Signature: Ensures token hasn't been altered

Format: header.payload.signature

📋 Standard JWT Claims

iss - Issuer of the token

sub - Subject of the token

aud - Audience for the token

exp - Expiration time (Unix timestamp)

nbf - Not valid before time

iat - Issued at time

jti - JWT ID (unique identifier)

❓ Frequently Asked Questions

What is JWT decoding and why do I need it? JWT decoding is the process of extracting and viewing the contents of a JSON Web Token without verification. It reveals the header and payload data, helping developers debug authentication issues, inspect token claims, and understand token structure. This is essential for API development, troubleshooting authentication flows, and ensuring your tokens contain the correct information. Our tool makes this process instant and secure, processing everything locally in your browser. How do I decode a JWT token online safely? Our JWT decoder processes everything locally in your browser using JavaScript. Simply paste your token into the input field, and it instantly decodes the header and payload. Your tokens and secret keys never leave your device, ensuring complete privacy and security. No server-side processing means your sensitive data stays private. The tool works offline once loaded, providing an additional layer of security for handling sensitive authentication tokens. What is the difference between JWT encoding and signing? JWT encoding converts JSON data into Base64URL format to create the token structure - it's simply a data transformation. JWT signing adds a cryptographic signature using a secret key (for HS256/HMAC algorithms) or private key (for RS256/RSA algorithms) to ensure the token hasn't been tampered with. Encoding creates the token format that can be transmitted safely, while signing provides security and integrity verification. Always use proper signing in production environments. How can I verify a JWT signature online? To verify a JWT signature, enter your token and the secret key used to sign it. Click the "Verify Signature" button, and the tool recalculates the signature using your provided key and compares it with the token's existing signature. If they match, the token is valid and unaltered. For RS256 tokens, you'll need the public key for verification. This verification process ensures that the token hasn't been modified since it was created, which is crucial for security. What are JWT claims and which ones are standard? JWT claims are pieces of information asserted about the token subject. Standard (registered) claims include: iss (issuer) identifies who created the token, sub (subject) identifies the token's subject, aud (audience) identifies intended recipients, exp (expiration time) sets when the token expires, nbf (not before) sets when the token becomes valid, iat (issued at) records creation time, and jti (JWT ID) provides a unique identifier. You can also add custom claims for application-specific data, but avoid storing sensitive information as JWT payloads are only encoded, not encrypted. How do I generate a secure JWT secret key? Use our built-in secret key generator to create cryptographically secure keys. For HS256, use at least 256 bits (32 characters) of random data. For stronger security with HS384 or HS512, use 384 or 512 bits respectively. For RS256/RS512, generate proper RSA key pairs with at least 2048-bit keys. Never use weak secrets like "secret" or "password". Store keys securely in environment variables, rotate them regularly, and never commit them to version control. Our generator creates cryptographically secure random keys suitable for production use. Can I check if my JWT token has expired? Yes! Our tool automatically checks the exp (expiration) claim against the current time. It also validates nbf (not before) and iat (issued at) claims to ensure token validity. The status indicator shows whether your token is valid, expired, or not yet active. Click "Check Expiration" for detailed timing information. This helps prevent using outdated tokens in your applications and assists in debugging authentication issues. The tool displays exact timestamps and calculates time differences for easy troubleshooting. What algorithms are supported for JWT signing and which should I use? We support HS256, HS384, HS512 (HMAC with SHA), RS256, RS384, RS512 (RSA with SHA), and none (unsecured - never use in production). HS algorithms use symmetric keys where the same key is used for both signing and verification - ideal for server-to-server communication. RS algorithms use asymmetric keys where a private key signs and a public key verifies - perfect for distributed systems where you don't want to share secrets. HS256 is most common for simple applications, while RS256 is preferred for microservices and public APIs. Choose based on your security requirements and architecture.

💡 Pro Tips: Always validate tokens server-side, use HTTPS for token transmission, implement token refresh mechanisms, and store tokens securely in your applications. Need help or have suggestions? Visit our Support Center for assistance.