Free JWT Decoder
Decode and inspect JSON Web Tokens instantly
Paste a JWT to decode its header and payload, inspect claims like expiration, issuer, and audience, and get a detailed security analysis of the token's algorithm and configuration. No data is sent to any server for basic decoding — it runs entirely in your browser.
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How it works
How JWT Decoder works
Paste your token
Paste any JSON Web Token into the input field. Tokens from authorization headers, cookies, or API responses all work.
Instant client-side decode
The header and payload are decoded entirely in your browser using base64 — nothing is sent to a server. You see the algorithm, claims, and timestamps immediately.
Get a security analysis
Click "Get Security Analysis" for an expert breakdown of the token's algorithm strength, claim configuration, and potential security issues.
Features
What JWT Decoder checks
Decode JWT header and payload instantly
View the full JSON structure of both the header (algorithm, type) and payload (claims, custom data) with syntax-highlighted output.
Inspect expiration and timestamp claims
Automatically parses iat, exp, and nbf timestamps into human-readable dates and shows whether the token is currently valid or expired.
Detect weak signing algorithms
Flags insecure algorithms like "none", HS256 used where RS256 is appropriate, and other algorithm confusion risks that lead to authentication bypasses.
Identify sensitive data in payloads
Checks for personally identifiable information, credentials, or internal system details that shouldn't be exposed in a JWT payload since tokens are only encoded, not encrypted.
Use cases
Who should use the free JWT Decoder
Developers
Debug authentication issues by inspecting JWT claims, expiration, and algorithm configuration during development and testing.
Security Engineers
Audit JWTs from production systems to verify tokens use strong algorithms, don't contain sensitive data, and have appropriate expiration policies.
Penetration Testers
Analyze intercepted tokens during engagements to identify algorithm confusion, missing claims, and other JWT vulnerabilities that could lead to auth bypass.
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Frequently asked questions
Everything you need to know about the free JWT Decoder.
Go beyond JWT Decoder
This free JWT Decoder checks a handful of things. Maced's AI pentest checks thousands.
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Proof of exploit on every finding · SOC 2 & ISO 27001 compatible