JWT Decoder FREE
Decode and inspect JSON Web Tokens locally in your browser. Check headers, claims, expiration and timing without exposing token data.
Standard compact JWT serialization: header.payload.signature
Paste a JWT to inspect its contents
Paste a compact JSON Web Token above to inspect its decoded header, payload claims, expiration timing, and signature structure immediately in your browser.
Token overview
Decoded Header
Decoded Payload
Registered Claims Inspector
Standard IANA / RFC 7519 registered claims found in the token payload.
| Claim | Meaning | Value | Interpretation |
|---|
No registered RFC 7519 claims found in this payload. Custom claims are visible in the Decoded Payload above.
Signature Segment
This tool decodes the JWT locally for inspection but does not verify its cryptographic signature. Decoding reveals the token content, but only your authentication server using its secret or public key can confirm whether the token is authentic and unaltered.
Security & Privacy Guidelines
- Zero server exposure: Tokens pasted into this tool remain strictly in browser memory. POLPROG does not upload, log, or persist token data to any server, storage, or telemetry system.
- Sensitive information: JWTs are base64-encoded, not encrypted (unless JWE is used). Anyone with access to the token string can read its payload contents. Never store sensitive secrets, passwords, or PII in standard JWT claims.
- Avoid sharing production tokens: Do not share active session or access tokens in public chats, tickets, or bug reports. Always invalidate compromised tokens on your identity provider.
What this inspection covers
In-browser decoding without key verification
The inspector validates JWT compact structure, decodes Base64URL header and payload, checks timing claims and algorithm headers. It does not perform cryptographic signature validation.
FAQ
Does POLPROG send my JWT token to a server?
No. The entire decoding process happens exclusively in your browser using client-side JavaScript. Tokens are never uploaded, logged, tracked, or saved in storage.
Does decoding a JWT prove that it is valid and authentic?
No. Decoding unpacks the Base64URL-encoded header and payload to reveal their contents. Proving authenticity requires verifying the cryptographic signature with the appropriate secret or public key, which this client-side inspector intentionally does not do.
What does alg: none mean?
The "none" algorithm indicates an unsecured JWT with no cryptographic signature. While permitted by RFC 7519 for specific internal debugging use cases, it provides no tamper protection and must never be accepted in secure authentication flows.
How are exp, iat, and nbf timestamps interpreted?
These claims represent Unix timestamps (seconds since 1 January 1970 UTC). The tool compares them against the current time to determine whether the token has expired, when it was issued, and whether it has reached its activation window.
Cybersecurity Basics for Business Websites and Web Applications
Most incidents are not sophisticated attacks. They are old problems, outdated software, reused passwords, exposed admin panels, that never got addressed. These are the fundamentals that prevent the majority of trouble.
Moment.js vs date-fns: Best Date Library for Modern Apps
Moment.js was once the default date library for JavaScript applications, but modern frontend stacks usually need smaller, more modular, and more tree-shakeable tools. date-fns provides date utilities as independent functions, which makes it a better fit for many modern apps. The decision is usually straightforward for new projects: Moment.js may remain in legacy code, but date-fns is often a better choice for new development.
Lodash vs es-toolkit: Modern Utility Library Comparison
Lodash is one of the most widely used utility libraries in the JavaScript ecosystem, especially in older and enterprise codebases. es-toolkit is a modern alternative built around TypeScript, ES modules, tree-shaking, and smaller bundles. The question is not whether Lodash still works. It does. The better question is whether your project still needs the weight and legacy patterns that come with it, or whether a leaner, type-first option fits your stack better in 2026.
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