JWT decoder and encoder for headers, payloads and token claims

What is JWT Decoder / Encoder?

A JWT decoder reads the Base64URL-encoded header and payload of a JSON Web Token. A JWT encoder can regenerate a test token from edited header and payload data.

Main use case: Decode a JWT, inspect claims such as exp or aud, edit test payloads and regenerate HS256 tokens for API debugging.

Common use cases

API debugging

Read token claims while investigating authentication issues.

Expiration checks

Inspect exp, iat and nbf timestamps before testing access flows.

Test token generation

Regenerate an HS256 token after editing test header or payload data.

Auth documentation

Prepare readable token examples for integration notes.

How to use the tool

1. Paste the JWT token.
2. Inspect the decoded header and payload.
3. Edit test claims if needed.
4. Optionally enter a HS256 secret.
5. Regenerate the encoded test token.

Best practices

• Use realistic test values when validating forms, exports or API payloads.
• Keep real customer, banking and production secrets out of public tools.
• Check the output format before copying it into a production workflow.
• Document whether a value is generated, validated, converted or only estimated.

Common mistakes

Confusing valid format with real-world validity

A generated or locally validated value can match a format without proving that it exists in an official system.

Using real production data

Public utilities are best for test data, demos, fixtures, QA and quick checks, not for confidential values.