JWT Decoder
Parse and decode JSON Web Tokens to analyze their structure and content. Secure, fast, and completely free.
JWT Decoder
Parse and decode JSON Web Tokens to analyze header, payload, and signature information. View standard, timing, and custom claims securely in your browser.
Key Features
Professional-grade tool designed for speed, security, and simplicity
Decode JWTs instantly
Paste a token and view the header, payload, and signature parts in a readable JSON view.
Security hints
Warnings for unsigned tokens, weak algorithms, expired tokens, and common misconfigurations.
No network uploads
All decoding is performed locally in your browser; nothing is sent to our servers.
Copy & export
Easily copy decoded JSON or export claims for debugging and audits.
Support for common formats
Handles standard compact serialized JWTs and common variations used in web apps and APIs.
How the JWT Decoder Works
The decoder splits the compact token into three base64url parts, decodes the JSON content, and displays structured information with useful checks.
Split token
A JWT is split by dots into header.payload.signature.
Base64url decode
Header and payload are base64url-decoded and parsed as JSON for easy inspection.
Analyze claims
The tool surfaces common claims (iss, sub, aud, exp) and warns about expired or malformed values.
Signature notes
The decoder shows the signature section but cannot verify it without a key — it will flag tokens using 'none' or weak algorithms.
When to use the JWT Decoder
Debugging auth issues
Inspect claims and expiration times when users report authentication failures.
Security reviews
Quickly check tokens for insecure algorithms (like 'none') or expired tokens during audits.
Learning & tutorials
Great for developers learning about JWT structure and common claim patterns.
Understanding JSON Web Tokens (JWTs)
A practical guide to JWT structure, common security trade-offs, and actionable best practices you can apply today.
What is a JWT?
JSON Web Tokens are compact, URL-safe tokens that encode claims as JSON. They are widely used to represent identity and authorization data between services and browsers.
Header & Algorithms
The header specifies metadata such as the signing algorithm (alg). Prefer asymmetric algorithms like RS256 or ES256. Do not accept tokens with the 'none' algorithm and be cautious with HS256 when secrets are shared across services.
Claims & Expiry
Standard claims include exp (expiration), iat (issued at), iss (issuer) and aud (audience). Always validate exp and aud server-side to reduce the risk of replay and token misuse.
Signature & Verification
The signature protects integrity and requires the issuers key to verify. This decoder shows the signature but cannot verify it without the appropriate cryptographic key.
Common Pitfalls
Avoid placing sensitive data in JWT payloads, accepting unsigned tokens, or relying solely on client-side checks. Use short-lived tokens with refresh flows for long sessions.
Best Practices
Use short expirations, validate issuer and audience, rotate keys regularly, and prefer asymmetric signing when tokens are exchanged across systems.
Understanding JWT Structure
Learn about the three parts of a JSON Web Token
Header
Contains metadata about the token, including the signing algorithm (alg) and token type (typ). Common algorithms include HS256, RS256, and ES256.
Payload
Contains the claims - statements about an entity and additional data. Includes standard claims like iss (issuer), exp (expiration), and sub (subject).
Signature
Used to verify the token hasn't been tampered with. Created by encoding the header and payload with a secret key using the specified algorithm.
Common JWT Claims
Standard claims you'll find in JWT payloads
Standard Claims
Timing Claims
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