About JWT.io
JWT.io is an online debugger for JSON Web Tokens, the compact format used to pass claims between two parties. You can paste a token, read its contents and check its signature.
What it does
The decoder splits a token into its header and payload and shows each part as readable JSON. If you enter the secret or key, it checks whether the signature matches. The encoder builds new tokens from edited claims, which is useful for testing how your application handles them.
Key features
- Decode a token into header, payload and claims
- Verify a signature using a secret key
- Encode new tokens with a chosen signing algorithm
- Claims breakdown for standard fields
- Example token generator for testing
- Links to passkey, OIDC and SAML test tools
Who it's for
Backend developers working on login and API authentication, testers checking token handling and students learning how JWTs are built. It is useful when a token is rejected and you need to see why.
Pricing and good to know
The debugger is free to use in the browser. The site is presented by Auth0, part of Okta, which also publishes a free JWT handbook and a list of libraries. Do not paste production secrets or live tokens into any website, even a trusted one, and use test values wherever possible.
Highlights
- Decode a token into header, payload and claims
- Verify a signature using a secret key
- Encode new tokens with a chosen signing algorithm
- Claims breakdown for standard fields
- Example token generator for testing
- Links to passkey, OIDC and SAML test tools
