JWT Decoder
Decode and inspect JSON Web Tokens with expiration status and claim details.
Paste a JWT token above to decode it
About JWT
Structure
JWTs consist of three parts: Header (algorithm & type), Payload (claims), and Signature (verification). Separated by dots.
Common Claims
Standard claims include: iss (issuer), sub (subject), exp (expiration), iat (issued at), aud (audience).
Expiration
The exp claim contains a Unix timestamp. This tool shows real-time expiration status with countdown.
Security Note
This tool only decodes JWTs for inspection. It does not verify signatures or validate token authenticity.
All decoding happens locally in your browser. No data is sent to any server.
Technical Specification
JWT Token Decoding & Payload Inspection Engine
Overview
The ToolsForges JWT Decoder parses and displays the contents of JSON Web Tokens, revealing the header, payload, and signature components that are normally obscured by Base64 encoding. Paste a complete JWT string to receive an instantly decoded view of the token's algorithm, issuer, subject, expiration timestamp, custom claims, and signature metadata.
Feature Specifications
- Header and Payload ParsingDecode both the JWT header and payload sections, displaying algorithm information, token type, and all embedded claims in a structured, readable format with proper JSON formatting.
- Timestamp ConversionAutomatically convert numeric iat (issued at), exp (expiration), and nbf (not before) claims into human-readable date and time strings, making token lifecycle validation immediate.
- Signature DisplayDisplay the encoded signature component separately for manual verification, alongside the algorithm used for signing, enabling developers to confirm token integrity.
- Claim Validation IndicatorsHighlight expired tokens, not-yet-valid tokens, and missing required claims with visual indicators, enabling quick token validity assessment at a glance.
Architecture
The decoder uses React useState for JWT input and the browser's atob() function for Base64 decoding of header and payload sections. The parsed JSON is displayed in a formatted structure with automatic timestamp conversion and validation indicators.
Frequently Asked Questions
Can this tool verify JWT signatures?
The tool displays the signature component but does not cryptographically verify it, as signature verification requires the signing key. Use server-side verification with the appropriate key.
What JWT formats are supported?
The tool supports standard three-part JWTs (header.payload.signature) using Base64URL encoding. Both JWS and JWE token structures are recognized.
Does this work with expired tokens?
Yes. Expired tokens are decoded and displayed with a visual indicator showing that the expiration timestamp has passed. This is useful for debugging authentication issues.
Is my token data stored?
No. All JWT strings, decoded headers, payloads, and signatures are processed entirely within your browser. No authentication tokens are transmitted to external servers.