I Built JWTLens: A Burp Suite Extension to Detect JWT Security Weaknesses

JWTs are everywhere.

They power authentication, session handling, API access, and secure communication across modern web applications. But JWT implementations are often misunderstood, misconfigured, or only partially validated. That is exactly where security issues start.

I built JWTLens, an open-source Burp Suite extension for JWT security testing, to help security engineers, pentesters, and bug bounty hunters inspect, analyze, and test JWTs faster.

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What JWTLens does

JWTLens helps you analyze JWTs during security testing and spot common weaknesses such as:

• algorithm confusion
• signature bypass attempts
• weak validation logic
• header manipulation
• missing or inconsistent claims checks
• passive JWT exposure in requests

Instead of manually decoding tokens and switching between tools, JWTLens brings JWT analysis directly into your Burp Suite workflow.

Why JWT security still matters

A JWT is only as strong as the validation around it.

Even when a token looks signed and valid, the application may still be vulnerable if it:

• trusts the wrong algorithm
• fails to verify claims properly
• accepts tampered headers
• assumes signature validation is enough
• exposes sensitive data in the payload

That is why JWT testing is still a valuable part of application security assessments.