JWT Decoder & Inspector — In-Browser Token Debugger & Claims Studio
Developer Tools
Loading tool...
About This Tool
Free, private, client-side JWT decoder and inspector studio. Decode JSON Web Tokens instantly to view the header, payload claims, and signature. Real-time expiration status, RFC 7519 claim descriptions, and Unix epoch translation — 100% in your browser.
How to Use
- Paste your JWT token into the primary input textarea.
- Click Decode JWT to instantly parse header, payload, and signature segments.
- Review the Claims Table for a breakdown of each claim with human-readable RFC descriptions.
- Check the Status Badge to verify whether the token is currently active or expired.
- Copy formatted JSON payloads directly to your clipboard.
Frequently Asked Questions
What is a JSON Web Token (JWT) and how is it structured?
A JSON Web Token (JWT) is an open, industry-standard RFC 7519 method for securely representing claims between two parties. Structurally, a compact JWT consists of three Base64URL-encoded strings separated by dots: (1) the JOSE Header, detailing the token type and cryptographic algorithm; (2) the Claims Payload, containing identity attributes, user roles, and expiration timestamps; and (3) the Cryptographic Signature, which verifies that the token was signed by a trusted issuer and has not been tampered with.
Does this in-browser tool verify cryptographic JWT signatures?
No. This tool intentionally focuses on decoding, inspecting, and auditing the readable contents of the token. Verifying a cryptographic signature mathematically requires knowledge of the secret key (for symmetric algorithms like HS256) or the public certificate/JWKS endpoint (for asymmetric algorithms like RS256). For security reasons, you should never input or expose private cryptographic signing keys in a browser utility.
Is a JWT token encrypted or can anyone read its contents?
A standard JWT (JSON Web Signature or JWS) is cryptographically signed, but it is NOT encrypted. The payload is simply serialized into Base64URL text, which can be decoded into plain readable JSON by anyone in possession of the string. You should never store sensitive personal data, unhashed passwords, API secrets, or confidential business records inside standard JWT payloads without applying nested encryption (JSON Web Encryption or JWE).
How does the inspector determine if a token is expired?
The inspector parses the standard 'exp' (Expiration Time) claim within the payload, which records an integer Unix timestamp in seconds. The tool compares this numeric value against your computer's local clock in real time (Date.now() / 1000). If the current timestamp is greater than the 'exp' value, the tool flags the token with an Expired status badge and displays the elapsed time.
What are standard IANA registered claims and how are they used?
RFC 7519 defines seven core registered claim names designed to provide interoperable identity metadata: 'iss' (Issuer, identifying who created the token), 'sub' (Subject, identifying the user or entity), 'aud' (Audience, identifying intended recipient services), 'exp' (Expiration time), 'nbf' (Not Before time), 'iat' (Issued At timestamp), and 'jti' (JWT unique ID to prevent replay attacks). Our tool automatically identifies these claims and displays human-readable descriptions for each.
Why is my JWT token failing to decode or reporting an invalid format?
The most common causes of decoding failures include: (1) copying extraneous prefixes such as the word 'Bearer ' along with the token; (2) missing dot delimiters or truncated strings caused by console line wrapping; (3) non-Base64URL characters introduced during copy-pasting; or (4) invalid, malformed JSON inside the original unencoded payload. Ensure you copy the complete raw token string starting from the first character of the header through the last character of the signature.
Is it safe to paste confidential production authentication tokens into this tool?
Yes, it is 100% secure. The JWT Decoder operates entirely within your local browser's isolated JavaScript memory sandbox. No token data, header values, or claims payloads are ever transmitted over external networks or persisted to remote databases. Furthermore, the application does not write data to local storage or cookies, ensuring that your tokens are immediately erased when the tab is closed.
Can this tool decode international UTF-8 characters and multi-language claims?
Yes. Our decoding engine utilizes full UTF-8 byte stream deserialization rather than basic Latin-1 string conversion. This ensures that international multilingual claims—including Arabic names, accented characters, Cyrillic text, and East Asian scripts—are decoded and displayed with 100% fidelity without character corruption or garbled symbols.
Guides & Tutorials
In-depth guides for every tool. Learn how to process your data privately, for free, right in your browser.
Read more