JWT Decoder and Inspector

Decode and inspect JWT tokens online. View header, payload, and signature, validate claims, and check expiry or algorithms. Free and private.

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About JWT Decoder and Inspector Tool

JWT Decoder and Inspector – Understand and Validate JSON Web Tokens

Experience

If you work with APIs or authentication systems, you’ve already encountered JSON Web Tokens (JWT). They are widely used for secure stateless authentication, carrying claims about users and sessions in a compact format. But JWTs can be tricky to debug. When tokens stop working, or when you need to verify the claims inside, manually inspecting them is both time-consuming and error-prone.

The JWT Decoder and Inspector Tool at FreeAiToolsOnline.com solves this problem. It lets you paste or upload a token and instantly decode its header, payload, and signature into readable JSON. Developers can verify claims, QA testers can confirm token structure, and security researchers can validate algorithms and expiry information — all without writing code or exposing sensitive data to external servers.

Expertise

This tool breaks down JWTs into their three core parts:

Header – reveals algorithm and token type (alg, typ).
Payload – shows claims such as iss (issuer), exp (expiry), iat (issued at), sub (subject), and custom fields.
Signature – confirms the token’s integrity when validated with a secret or public key.

Key capabilities include:

Base64URL decoding of header and payload.
Human-readable JSON formatting.
Validation of expiration (exp) and not-before (nbf) claims.
Optional signature verification (paste secret or key).
Algorithm identification to highlight secure vs weak choices.
Copy, download, print, and share decoded data.

Authoritativeness

JWTs are part of the IETF RFC 7519 standard and are fundamental in OAuth 2.0, OpenID Connect, and modern API security. This tool aligns with best practices used by developers and security engineers in professional environments. It not only decodes tokens but also provides contextual hints (e.g., “Token expired 2 hours ago” or “Algorithm is HS256 — secure but requires strong secrets”).

Because it combines decoding, inspection, and validation, the tool acts as a reliable reference for anyone who needs to understand JWTs — from backend developers to penetration testers.

Trustworthiness

All decoding happens directly in your browser. Tokens are never uploaded to any server, keeping your secrets safe. Clear messages explain the meaning of each field and highlight potential risks (like missing expiry). Users retain full control over their input, and autosave remembers the last token for convenience.

The interface is modern, responsive, and transparent: input on one side, decoded results on the other. Pastel feature cards summarize the most important checks: structure validity, claim verification, and signature status.