JWT Builder & Signer

Free

Build and sign JWTs with HS256/384/512. Verify signatures. Runs in your browser.

Rate this tool

What is JWT Builder & Signer?

Updated July 25, 2026

Build, sign, and verify JSON Web Tokens (JWT) entirely in your browser. Choose HMAC algorithm (HS256, HS384, or HS512), set any standard or custom claims, enter a secret key, and get a signed JWT instantly. Switch to Verify mode to validate any JWT signature. Uses the Web Crypto API — your secret never leaves your device.

jwtjson web tokenjwt builderjwt signerjwt verifierhs256hs512token generator

Why choose JWT Builder & Signer?

The JWT Builder & Signer allows developers to quickly generate, sign, and verify JSON Web Tokens directly in the browser using the Web Crypto API. Because processing happens entirely client-side, secret keys and token payloads never leave your local device, ensuring complete data privacy without requiring software installation or account registration.

Best for

Developers debugging API authentication flows
Testing custom token claims and signatures locally
Verifying JWT signatures without exposing secrets to third-party servers

Good to know: This tool is limited to HMAC algorithms (HS256, HS384, HS512); workflows requiring asymmetric algorithms like RSA or ECDSA will need a different approach.

How to Use JWT Builder & Signer

Create, sign, and verify secure JSON Web Tokens using HMAC algorithms directly in your browser.

1
Select your HMAC signing algorithm
Choose between HS256, HS384, or HS512 from the algorithm dropdown menu to define the cryptographic hash function.
2
Configure your standard and custom claims
Enter the JSON payload including standard claims like sub or exp, or add any custom data fields required for your token.
3
Enter your secure secret key
Input the secret string used to sign the token; the Web Crypto API ensures this key never leaves your local device.
4
Generate and copy the signed JWT
The tool instantly builds and signs the token. Copy the resulting three-part encoded string for use in your application.
5
Verify an existing JWT signature
Switch to Verify mode and paste a token to validate that its signature matches the provided secret key.

Estimated time: PT1M

Frequently Asked Questions

What is the JWT Builder & Signer tool used for?

This tool allows you to create, sign, and verify JSON Web Tokens (JWT) directly in your web browser. You can configure standard or custom claims and apply digital signatures using HMAC algorithms like HS256, HS384, or HS512.

How do I create a signed JWT with this tool?

To generate a token, enter your desired payload claims and a secret key into the interface, then select your preferred HMAC algorithm. The tool uses the Web Crypto API to instantly produce a signed JWT string ready for use in your applications.

Is my secret key safe when using this JWT builder?

Yes, your data privacy is a priority as the tool runs entirely client-side in your browser. Because it utilizes the Web Crypto API, your secret key and payload never leave your device or get transmitted to a server.

Can I verify an existing JWT signature with this tool?

Yes, the tool includes a dedicated Verify mode specifically for validating signatures. Simply input the JWT and the corresponding secret key to confirm if the signature is valid and the token remains untampered.

What algorithms are supported for signing tokens?

The JWT Builder & Signer currently supports the HMAC family of algorithms, specifically HS256, HS384, and HS512. These are standard symmetric-key algorithms used for securing JSON Web Tokens.

Is there a cost to use the JWT Builder & Signer?

This is a free security tool with no credit costs for users. Anonymous users can perform up to 200 operations, while authenticated users have a higher rate limit of 1,000 operations.

Does this tool require any software installation?

No installation is required as the tool is a web-based utility that runs in any modern browser. It is designed to be a lightweight, instant solution for developers needing to test or generate JWTs on the fly.