Unsigned JWT Builder

How it works

Your header and payload JSON objects are validated and Base64url-encoded independently, then joined as header.payload with an empty trailing signature segment—exactly the shape of a real alg=none JWT. No cryptographic signing operation is ever performed, even if the header claims an algorithm like HS256, to make the point that a JWT's header is unverified metadata.

Benefits

• Clear, hands-on demonstration of JWT structure
• Illustrates why the alg header claim can never be trusted blindly
• Runs entirely client-side—no network calls
• Useful for building test fixtures for claim-reading (not verification) code

Use cases

• Teach students or new engineers how JWTs are structured
• Demonstrate historical alg=none and alg-confusion vulnerabilities
• Generate test fixtures for parsers that only read claims in trusted test environments
• Show why signature verification must happen server-side, independent of header claims

Best practices

• Never accept alg=none tokens in any production authentication or authorization system
• Always pin the expected signing algorithm server-side instead of trusting the token header
• Use this tool only in learning, testing, or security-training contexts
• Pair this demo with a real signing tool (like HMAC Generator) to show the contrast

Common mistakes

• Mistaking an unsigned demo token for something a real server should accept
• Assuming setting alg to a strong algorithm in the header makes a token trustworthy
• Using output from this tool against a real, production authentication endpoint
• Forgetting that claims in an unsigned token can be changed by anyone with no detection

Privacy

Token construction happens entirely client-side—no header or payload data is uploaded to ToolHub. Because the payload may resemble real claims, on-device history requires explicit opt-in.