Decode JWT header and payload, check algorithm security, expiration, missing claims, and common misconfigurations. All local. Nothing is transmitted.
Decodes JWT header and payload, checks algorithm, expiration, missing claims, and common misconfigurations. Nothing is transmitted. All local.
Decodes a JSON Web Token (JWT) client-side and displays the header, payload, and signature components in readable format. Highlights security-relevant fields: algorithm, expiration, issuer, audience, and any custom claims. Checks for known-weak configurations like the none algorithm or algorithm confusion patterns.
Decoding happens entirely in your browser — no token data is transmitted anywhere.
JWT vulnerabilities are a consistent finding in API security assessments. The most common issues are algorithm confusion (accepting RS256 tokens verified as HS256), the none algorithm accepting unsigned tokens, missing expiration validation, and overly broad scope or role claims.
Before using a JWT in a security review or code audit, decode it to understand what claims it contains, how long it is valid for, and what algorithm it uses. A token that never expires or uses a symmetric algorithm with a guessable secret represents a significant authentication risk.