Free JWT Generator & Decoder

Generate, encode, decode, and debug JSON Web Tokens instantly. Perfect for API authentication testing and development.

JWT Generator & Decoder

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What is a JWT?

A JWT (JSON Web Token) is an open standard (RFC 7519) for securely transmitting information between parties as a JSON object. JWTs are commonly used for authentication and authorization in web applications and APIs.

Each JWT consists of three parts separated by dots: Header (algorithm and token type),Payload (claims/data), and Signature (verification). The token is Base64Url encoded, making it compact and URL-safe.

JWTs are self-contained - they carry all the information needed for verification, reducing the need for database lookups. This makes them ideal for stateless authentication in microservices and distributed systems.

Powerful JWT Features

Everything you need to create, validate, and debug JSON Web Tokens for your applications.

Multiple Algorithms

Support for HS256, HS384, and HS512 HMAC algorithms with secure signing.

Signature Verification

Verify JWT signatures instantly with your secret key to ensure token integrity.

Token Debugger

Decode and inspect any JWT to view its header, payload, and signature components.

Expiration Tracking

Automatic detection of expired tokens with human-readable timestamp display.

Auto Timestamps

One-click refresh of iat and exp claims with configurable expiration times.

Visual Structure

Color-coded token display showing header, payload, and signature sections.

Easy Copy & Download

Copy generated tokens to clipboard or download as text file instantly.

Client-Side Processing

100% browser-based - your secrets never leave your device for maximum security.

How to Use the JWT Generator

🔐 Generating a JWT Token

  1. Select Algorithm: Choose your signing algorithm (HS256, HS384, or HS512). HS256 is most commonly used.
  2. Set Secret Key: Enter your secret key or click the refresh button to generate a secure random key.
  3. Edit Payload: Modify the JSON payload with your custom claims. Standard claims include:
    • sub - Subject (user ID)
    • iat - Issued At (timestamp)
    • exp - Expiration Time (timestamp)
    • name, email, role - Custom claims
  4. Generate: Click "Generate JWT" to create your signed token.
  5. Copy or Download: Use the token in your API requests or save it for later.

🔍 Decoding & Debugging a JWT

  1. Switch to Decode Tab: Click on "Decode & Debug" tab.
  2. Paste Token: Enter the JWT you want to analyze. The token will be automatically decoded.
  3. View Components: See the decoded header, payload, and signature with color-coded sections.
  4. Verify Signature (Optional): Enter the secret key to verify the token's signature is valid.
  5. Check Timestamps: View when the token was issued and when it expires in human-readable format.

📋 Standard JWT Claims Reference

ClaimNameDescription
issIssuerWho created and signed the token
subSubjectThe user or entity the token represents
audAudienceIntended recipients of the token
expExpirationUnix timestamp when token expires
nbfNot BeforeToken not valid before this time
iatIssued AtWhen the token was created
jtiJWT IDUnique identifier for the token

Understanding JWT Structure

🔴 Header

Contains the token type and signing algorithm.

{
  "alg": "HS256",
  "typ": "JWT"
}

🟣 Payload

Contains claims (user data and metadata).

{
  "sub": "1234567890",
  "name": "John Doe",
  "iat": 1516239022
}

🔵 Signature

Verifies the token hasn't been tampered with.

HMACSHA256(
  base64UrlEncode(header) + "." +
  base64UrlEncode(payload),
  secret
)

Frequently Asked Questions

A JWT (JSON Web Token) is a compact, URL-safe token format for securely transmitting information between parties. JWTs are commonly used for authentication in web applications, APIs, and microservices. They're stateless, meaning servers don't need to store session data, making them ideal for scalable applications.

Yes! This tool runs entirely in your browser using the Web Crypto API. Your secret keys and tokens never leave your device - no data is sent to any server. This makes it safe for testing and development purposes. For production, always generate tokens on your secure backend.

These are all HMAC (Hash-based Message Authentication Code) algorithms using different SHA hash functions. HS256 uses SHA-256 (256-bit), HS384 uses SHA-384 (384-bit), and HS512 uses SHA-512 (512-bit). HS256 is the most commonly used and provides sufficient security for most applications. Higher variants offer more security but slightly larger signatures.

For HS256, use at least a 256-bit (32 bytes) secret key. For HS384, use at least 384 bits (48 bytes). For HS512, use at least 512 bits (64 bytes). The "Generate Random Secret" button creates a 256-bit cryptographically secure key suitable for HS256.

The "exp" (expiration time) claim is a Unix timestamp that defines when the token expires. After this time, the token should be rejected. Common practice is to set short expiration times (15 minutes to 1 hour) for access tokens and use refresh tokens for longer sessions.

Yes! The header and payload of a JWT are only Base64Url encoded, not encrypted. Anyone can decode and read them. The secret key is only needed to verify the signature and ensure the token hasn't been tampered with. Never put sensitive information in a JWT payload.

The token's "exp" claim timestamp is in the past. Click "Refresh Timestamps" when generating a new token to update both "iat" (issued at) and "exp" (expiration) to current time. The default expiration is set to 1 hour from generation.

This means the secret key you provided doesn't match the one used to sign the token. The signature is created by hashing the header and payload with the secret key. If any part is different, verification fails - this is how JWTs detect tampering.

This tool is designed for development, testing, and learning purposes. For production, generate JWTs on your secure backend using libraries like jsonwebtoken (Node.js), PyJWT (Python), or java-jwt (Java). Never expose your secret keys in client-side code.

There's no official limit, but JWTs are typically sent in HTTP headers which have practical limits (8KB for most servers). Keep payloads small - include only essential claims. Large payloads increase bandwidth usage and token processing time.

Free online JWT decoder, encoder, and generator. Decode JSON Web Tokens instantly, verify signatures, generate HS256/384/512 tokens, and inspect payload claims.

Tool
JWT Decoder & Generator
Category
All tools
Availability
Browser-based tool