JWT Decoder
Articles, guides, and in-depth tips for the JWT Decoder — everything you need to get the most out of it.
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JWT Claims: The Seven Registered Ones and Why aud Matters
Most JWT Libraries Don't Check the Audience Claim — What Gets Verified, What Doesn't, and How to Handle Revocation
JWT libraries automatically verify signatures and exp claims — but most don't check iss (issuer) or aud (audience) by default, which is why a token from service A can be used at service B if they share a signing key. Here's what each registered claim actually enforces, the three revocation approaches (short expiry + refresh tokens, jti blocklist, short expiry without refresh), and why JWT payloads are readable by anyone who holds the token.
JWT "Stateless" Is a Half-Truth — The Microservices Patterns That Account for the Other Half
JWTs are "stateless" — but deciding whether to trust the claims may require state, and confusing the two leads to architectural mistakes. Here's the microservices JWT validation dilemma (every service validates vs gateway-validates-services-trust), why encoding authorization roles in JWTs creates a stale-claims window problem, why the aud claim validation is commonly skipped (and why that's a vulnerability), and the mTLS + JWT separation of concerns that modern service meshes use.
JWT vs Opaque Session Tokens: Why This Tool Can Decode Some Tokens and Not Others
Some APIs return a token that decodes into readable claims; others return an opaque string that reveals nothing. The difference isn't a quality signal — it's the fundamental architectural choice between stateless JWTs (the token contains the session data) and stateful opaque tokens (the token is a lookup key into a server-side session store). Here's why instant revocation pushes some systems toward the "extra database lookup" approach, and what it means when a token you paste into this tool decodes to nothing.
JWT Token Refresh Strategies: Access Tokens, Refresh Rotation, and When Sessions Beat JWTs
Short-lived access tokens require a refresh mechanism — and how you implement that mechanism determines your app's security and user experience. Here's refresh token rotation, silent refresh in SPAs, theft detection via refresh token families, and the cases where server-side sessions are simpler and safer.
JWT Security Vulnerabilities: alg:none, Algorithm Confusion, and Secure Token Storage
The alg:none attack, RS256/HS256 algorithm confusion, weak HS256 secrets, localStorage vs httpOnly cookies, and revocation without statefulness — JWT security vulnerabilities are specific and avoidable. Here's how each one works and how to fix it.
JWT Decoder — Debug Authentication Errors by Inspecting Token Claims
Learn how to use a JWT decoder to debug 401 errors, understand the header, payload, and signature sections, check expiry and audience claims, and identify security issues like alg:none attacks.
JWT Decoder — Inspect Any JSON Web Token Instantly
Learn what's inside a JSON Web Token, how to read the header, payload, and expiration claims, and how to use a free JWT decoder to debug authentication issues instantly.
