What is JWT Generation?
JWT generation is the process of creating a signed JSON Web Token that can be used for authentication and authorization in web applications and APIs. A JWT generator takes a header (specifying the algorithm and token type), a payload (containing claims about the user and session), and a secret key, then produces a signed token string. The signature provides integrity — any modification to the header or payload invalidates the signature, ensuring the token's contents are trustworthy.
For development and testing, a quick JWT generator helps you create sample tokens without setting up a full authentication server. You can test your API endpoints, verify your JWT verification logic, and debug token-related issues. The tool supports HMAC-based algorithms (HS256, HS384, HS512) which use a shared secret key for both signing and verification — ideal for single-server and trusted-service scenarios.
JWT Signing Algorithms
| Algorithm | Hash Function | Signature Size | Use Case |
|---|---|---|---|
| HS256 | SHA-256 | 256 bits (32 bytes) | Default choice, excellent balance of security and performance |
| HS384 | SHA-384 | 384 bits (48 bytes) | Higher security when token size isn't a concern |
| HS512 | SHA-512 | 512 bits (64 bytes) | Maximum security, recommended for high-sensitivity applications |
Algorithm choice: HS256 is the recommended default for most development and testing scenarios. It provides strong security with minimal overhead. Choose HS512 when token size is not a concern and maximum security is desired.
Common Development Use Cases
API Testing
Generate test JWTs to validate your API's authentication middleware. Test token expiry, invalid signatures, and malformed tokens without a full auth server.
Prototype Authentication
Quickly create JWTs for prototype and MVP applications without building the full authentication flow. Perfect for early-stage development and demos.
Debugging Token Issues
Reproduce and debug JWT-related issues by generating tokens with specific claims, expiry times, or algorithm types to isolate problems in your verification logic.
Learning & Education
Learn how JWT structure and signing work by experimenting with different headers, payloads, and secret keys. See how changes affect the resulting token.
Step-by-Step: Generate a JWT Token
Enter the Header
Open the JWT Generator tool. The header is pre-filled with the default algorithm (HS256) and token type (JWT). You can customize the algorithm to HS384 or HS512 if needed.
Add Payload Claims
Enter the claims for your token as a JSON object. Include standard claims like sub (user ID), name, iat (issued at), and exp (expiration). You can also add custom claims for roles, permissions, or application-specific data.
Set Your Secret Key
Provide a secret key for HMAC signing. Use a strong, random key of sufficient length (at least 32 characters for HS256). The tool uses the Web Crypto API to sign the token securely in your browser.
Copy the Signed Token
Click generate to produce the signed JWT. The tool displays the complete token (header.payload.signature). Copy it and use it in your API requests via the Authorization header: Bearer <token>.
JWT Generation Examples
{"alg": "HS256", "typ": "JWT"}
Payload:
{"sub": "1234567890", "name": "John Doe", "iat": 1516239022, "exp": 1735689600, "role": "admin"}
Secret:
my-secret-key-at-least-32-chars-long
Result:
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiaWF0IjoxNTE2MjM5MDIyLCJleHAiOjE3MzU2ODk2MDAsInJvbGUiOiJhZG1pbiJ9.signature_here
Tip: Use JWT Decoder to verify your generated token. Paste the token back into the decoder to inspect the header and payload claims and confirm everything looks correct.
Best Practices for JWT Generation
- Use strong secret keys: For HMAC algorithms, use a cryptographically random secret key. For HS256, use at least 32 bytes (256 bits). For HS512, use at least 64 bytes (512 bits). Never use weak or guessable secrets.
- Include expiration claims: Always set the
expclaim with a reasonable expiration time. Short-lived tokens (15-60 minutes) limit the damage if a token is compromised. Use refresh tokens for longer sessions. - Never put secrets in payload: JWT payloads are Base64-encoded, not encrypted. Anyone with the token can read the claims. Store only non-sensitive data like user IDs and roles.
- Use appropriate algorithms: HS256 is suitable for development and single-server scenarios. For multi-service architectures, consider RS256 (asymmetric) so services can verify without sharing the signing key.
- Validate tokens server-side: Always validate JWTs on your server before trusting them. Check the signature, expiration, issuer, and audience claims. Never trust client-side validation alone.
- Rotate your secrets regularly: Periodically change your JWT signing secrets. Maintain a grace period where both old and new secrets are accepted to allow tokens signed with the old key to expire naturally.
Limitations to Consider
- Development and testing only: This tool is designed for generating JWTs for development, testing, and learning. For production authentication, use dedicated server-side JWT libraries that handle key management, algorithm validation, and security best practices.
- HMAC only: The tool supports HMAC-based algorithms (HS256, HS384, HS512). It does not support asymmetric algorithms like RS256 (RSA) or ES256 (ECDSA), which require public/private key pairs.
- No token revocation: The tool generates tokens but does not manage revocation. In production, implement a token blacklist or use short expiration times to handle scenarios where tokens need to be invalidated.
- Signature not validated: While the tool signs tokens, it does not validate them after generation. Always use a server-side library to verify tokens in your application.
Important security disclaimer: This tool is intended for development and testing purposes only. For production authentication systems, always use well-established server-side JWT libraries that implement proper key management, algorithm whitelisting, and signature validation. Generating JWTs in a browser for production use introduces unnecessary security risks.
Frequently Asked Questions
What is the difference between HS256, HS384, and HS512?
These are HMAC-based signing algorithms that differ only in the hash function used. HS256 uses SHA-256 (256-bit output), HS384 uses SHA-384 (384-bit output), and HS512 uses SHA-512 (512-bit output). HS512 offers the strongest security but produces longer signatures.
Can I use this tool for production authentication?
This tool is designed for development and testing purposes. For production use, always use a well-tested JWT library in your server-side language (such as jsonwebtoken for Node.js, PyJWT for Python, or java-jwt for Java) that handles key management, algorithm validation, and security best practices.
Is it safe to paste my secret key here?
Yes, all processing happens entirely in your browser. Your secret key is never sent to any server. However, for production systems, we recommend using server-side JWT libraries with proper key management rather than browser-based tools.
What claims should I include in a JWT?
At minimum, include sub (subject) to identify the user, iat (issued at) for when the token was created, and exp (expiration) with a reasonable lifetime. For authorization, include custom claims like roles or permissions. Avoid storing sensitive data as claims are only Base64-encoded.
Why use HMAC over RSA for JWT signing?
HMAC (HS256, HS384, HS512) uses a single shared secret for both signing and verification, making it simpler for single-server or trusted-party scenarios. RSA (RS256) uses a public/private key pair, enabling anyone with the public key to verify without being able to sign. Choose RSA when multiple services need to verify tokens.
Is my data private when using this tool?
Yes, all JWT generation happens entirely in your browser using the Web Crypto API. Your secret key and payload data are never transmitted to any server, keeping everything completely private and secure on your device.
Related JWT Tools
Complement your JWT workflow with these tools:
JWT Decoder
Decode and inspect JWT header, payload, and claims for debugging
Hash Generator
Generate MD5, SHA-1, SHA-256, and SHA-512 hashes for data integrity
UUID Generator
Generate UUID v4 strings for unique identifiers