JWT Builder
Compose a JWT from scratch — edit the header and payload JSON, choose HMAC-SHA256, and sign with your own secret key. All operations run in-browser using the Web Crypto API. Useful for testing API authentication, debugging token issues, and understanding the JWT format.
Runs in your browser
Nothing uploaded
Free, no signup
Ctrl + Enter to run · Recent brings back your last inputs · Everything stays in this browser
JWT Builder: questions
Is this safe to use with real secrets?
Yes — signing happens entirely in your browser via the Web Crypto API. Nothing is sent to any server. Treat any generated token as sensitive; don't paste real production secrets into untrusted online tools.
What is a JWT?
A JSON Web Token is a compact, URL-safe string encoding a JSON header, a JSON payload, and a cryptographic signature. The signature lets the server verify the payload hasn't been tampered with.
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