JWT Decoder - Free JSON Web Token Tool

Decode and analyze JSON Web Tokens instantly. View JWT header, payload, and signature for API development and security testing.

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About JWT Decoder Tool

What is a JWT Token?

JWT (JSON Web Token) is an open standard (RFC 7519) for securely transmitting information between parties as a JSON object. JWTs are commonly used for authentication and authorization in modern web applications and APIs. A JWT consists of three parts: Header (algorithm and token type), Payload (claims and data), and Signature (verification). JWTs are compact, URL-safe, and can be verified and trusted because they are digitally signed.

How to Use JWT Decoder

  1. Copy JWT Token: Get your JWT token from API response, browser storage, or authentication header.
  2. Paste Token: Paste the complete JWT token into the input field (including all three parts separated by dots).
  3. Decode: Click the "Decode JWT" button to analyze the token structure.
  4. View Results: Examine the decoded header, payload, claims, and expiration time.
  5. Verify Signature: Check signature validity and algorithm used for token signing.

Why Use JWT Decoder?

JWT decoder is essential for API development, debugging authentication issues, and security testing. It helps developers understand token structure, verify claims, check expiration times, and identify security issues. Without a JWT decoder, tokens appear as encoded strings making it impossible to inspect their contents. This tool is crucial for troubleshooting authentication problems, validating token claims, and ensuring proper JWT implementation.

JWT Token Structure

  • Header: Contains token type (JWT) and signing algorithm (HS256, RS256, etc.).
  • Payload: Contains claims (user data, permissions, expiration, issuer, etc.).
  • Signature: Verifies token integrity using secret key or public/private key pair.
  • Format: header.payload.signature (three Base64URL encoded parts separated by dots).
  • Common Claims: iss (issuer), sub (subject), aud (audience), exp (expiration), iat (issued at).

Who Should Use This Tool?

This JWT decoder is perfect for API developers, backend engineers, security professionals, QA testers, and DevOps engineers. Whether you're implementing authentication, debugging API issues, testing security, or learning about JWTs, this tool provides instant token analysis and validation.

Frequently Asked Questions (FAQs)

JWT (JSON Web Token) is a compact, URL-safe token format for securely transmitting information. It consists of three Base64URL-encoded parts: header (algorithm info), payload (claims/data), and signature (verification). JWTs are commonly used for authentication - after login, the server issues a JWT that the client includes in subsequent requests to prove identity.

JWT decoding is safe because JWTs are not encrypted - they're only Base64URL encoded and signed. Anyone can decode a JWT to view its contents. However, never paste production JWTs containing sensitive data into online tools. The signature verification requires the secret key, which should never be shared. Use this tool for development and testing only.

JWTs are stateless and self-contained (all data is in the token), while session tokens are stateful (server stores session data). JWTs don't require server-side storage, making them ideal for distributed systems and APIs. However, JWTs can't be easily revoked, while sessions can be terminated server-side. Each has its use cases depending on requirements.

JWT signature verification requires the secret key (for HMAC algorithms like HS256) or public key (for RSA algorithms like RS256). This tool can decode the token and show the algorithm used, but actual signature verification must be done server-side with the appropriate key. Never expose your secret keys publicly.

JWT claims are statements about an entity (typically the user) and additional metadata. Standard claims include: iss (issuer), sub (subject/user ID), aud (audience), exp (expiration time), nbf (not before), iat (issued at), and jti (JWT ID). You can also add custom claims for application-specific data like roles, permissions, or user details.

Yes! Expired JWTs can still be decoded to view their contents. The expiration (exp claim) is just data in the payload - decoding doesn't validate expiration. However, servers should reject expired tokens during authentication. This tool shows the expiration time so you can check if a token is expired.