Free JWT Decoder Online

Decode, verify, and debug JSON Web Tokens instantly. Analyze header, payload & signature with syntax highlighting.

100% Secure Instant Decode Client-Side Only Free Forever
HEADER: Algorithm & Token Type ALGORITHM & TOKEN TYPE 
{}
PAYLOAD: Data DATA 
{}
SIGNATURE VERIFY SIGNATURE
HMACSHA256( base64UrlEncode(header) + "." + base64UrlEncode(payload), your-256-bit-secret )

How to Use the JWT Decoder

Decoding JSON Web Tokens is quick and easy with our free online JWT decoder. Follow these simple steps:

  1. Paste your JWT token - Copy the complete JWT string (header.payload.signature format) and paste it into the input field. The token should be in the format: xxxxx.yyyyy.zzzzz
  2. View decoded results instantly - Our JWT parser automatically decodes and displays the header (algorithm and token type) and payload (claims and data) in formatted JSON with syntax highlighting.
  3. Check token expiration - If your JWT contains expiration (exp) and issued-at (iat) claims, we'll automatically display whether the token is still valid or expired.
  4. Analyze the signature - View the signature algorithm used and understand how the token is signed. Note: Signature verification requires the secret key which we don't store for security.
  5. Use sample token - Click "Sample Token" to load an example JWT and see how decoding works before using your own tokens.
Privacy Guaranteed: All JWT decoding happens 100% client-side in your browser. Your tokens never leave your device - we don't store, log, or transmit any token data to our servers.

What is a JSON Web Token (JWT)?

A JSON Web Token (JWT) is an open standard (RFC 7519) that defines a compact, self-contained way for securely transmitting information between parties as a JSON object. JWTs are widely used for authentication, authorization, and information exchange in modern web applications, RESTful APIs, and microservices architectures.

Header

The header typically consists of two parts: the type of token (JWT) and the signing algorithm (such as HS256, RS256, or ES256). This information is Base64Url encoded to form the first part of the JWT.

{
  "alg": "HS256",
  "typ": "JWT"
}
Payload

The payload contains the claims - statements about the user and additional data. Claims can be registered (like iss, exp, sub), public, or private claims defined by the application.

{
  "sub": "1234567890",
  "name": "John Doe",
  "iat": 1516239022
}
Signature

The signature is created by encoding the header and payload, then signing with a secret key (for HMAC) or private key (for RSA/ECDSA). This ensures the token hasn't been tampered with.

HMACSHA256(
  base64UrlEncode(header) + "." +
  base64UrlEncode(payload),
  secret
)

Common Use Cases for JWT Tokens

JSON Web Tokens are versatile and used across many authentication and authorization scenarios. Here are the most common applications:

User Authentication

JWTs are the backbone of modern stateless authentication. After login, a JWT is issued containing user identity and permissions. This token is sent with subsequent requests, eliminating the need for server-side sessions.

Keywords: JWT authentication, login tokens, bearer tokens
OAuth 2.0 & OpenID Connect

JWTs power OAuth 2.0 access tokens and OpenID Connect ID tokens. They enable secure authorization flows for single sign-on (SSO), social logins, and API authorization across multiple services.

Keywords: OAuth tokens, OIDC, access tokens, ID tokens
API Authorization

RESTful APIs and GraphQL endpoints use JWTs to verify client identity and permissions. The token's payload contains scopes and roles that determine what resources the client can access.

Keywords: API security, REST authentication, Bearer authorization
Microservices Communication

In microservices architectures, JWTs enable service-to-service authentication. Each service can verify the token without calling a central auth server, improving performance and reducing coupling.

Keywords: microservices auth, service mesh, distributed systems
Mobile App Authentication

Mobile applications use JWTs for secure API communication. Tokens are stored securely on the device and refreshed periodically using refresh tokens to maintain session continuity.

Keywords: mobile auth, app tokens, refresh tokens
Password Reset & Email Verification

JWTs are ideal for one-time use tokens in password reset links and email verification. The token can encode user ID and expiration, making verification stateless and secure.

Keywords: reset tokens, verification links, magic links

JWT Standard Claims Reference

The JWT specification defines several registered claims that provide standardized, interoperable claims. Understanding these claims is essential for properly decoding and validating JWT tokens:

Claim Name Description Example
iss Issuer Identifies the principal that issued the JWT. Typically the authentication server URL. "https://auth.example.com"
sub Subject Identifies the principal subject of the JWT. Usually the user ID or username. "user123"
aud Audience Identifies the recipients the JWT is intended for. Can be a single value or array. "api.example.com"
exp Expiration Time Unix timestamp after which the JWT must not be accepted. Critical for token security. 1735689600
nbf Not Before Unix timestamp before which the JWT must not be accepted for processing. 1704067200
iat Issued At Unix timestamp when the JWT was issued. Useful for determining token age. 1704067200
jti JWT ID Unique identifier for the JWT. Can be used to prevent token replay attacks. "abc123xyz"

JWT Signing Algorithms Explained

Our JWT decoder supports all standard signing algorithms. Understanding the algorithm used is crucial for proper JWT verification and security:

HMAC Algorithms
  • HS256 - HMAC using SHA-256 (most common)
  • HS384 - HMAC using SHA-384
  • HS512 - HMAC using SHA-512

Symmetric algorithms using a shared secret key. Fast and suitable for server-to-server communication.

RSA Algorithms
  • RS256 - RSA Signature with SHA-256
  • RS384 - RSA Signature with SHA-384
  • RS512 - RSA Signature with SHA-512

Asymmetric algorithms using public/private key pairs. Ideal when clients need to verify tokens.

ECDSA Algorithms
  • ES256 - ECDSA using P-256 and SHA-256
  • ES384 - ECDSA using P-384 and SHA-384
  • ES512 - ECDSA using P-521 and SHA-512

Elliptic curve cryptography - smaller keys with equivalent security to RSA. Efficient for mobile apps.

Frequently Asked Questions About JWT Decoding

A JSON Web Token (JWT) is an open standard (RFC 7519) for securely transmitting information between parties as a JSON object. JWTs are digitally signed using a secret (HMAC algorithm) or a public/private key pair (RSA or ECDSA). A JWT consists of three Base64Url-encoded parts separated by dots: the Header (algorithm and token type), Payload (claims and data), and Signature (verification hash). When you decode a JWT, you're converting these Base64Url-encoded strings back into readable JSON.

Yes, absolutely! Our JWT decoder is 100% secure because all processing happens entirely in your browser using JavaScript. Your tokens never leave your device and are never sent to our servers. We don't log, store, or have any access to the tokens you decode. This client-side approach makes it completely safe for decoding production tokens, access tokens, and other sensitive authentication data. However, we recommend never sharing JWT tokens publicly as the payload is only encoded, not encrypted.

Our decoder analyzes and displays the signature algorithm and format, but signature verification requires the secret key (for HMAC) or public key (for RSA/ECDSA). Since we prioritize security and never ask for your secret keys, signature verification must be done server-side or with separate tooling. This decoder is ideal for inspecting token structure, checking claims, and debugging - but production signature verification should happen in your application code.

Our JWT decoder automatically detects and displays token expiration status. Look for the exp (expiration) claim in the decoded payload - this is a Unix timestamp indicating when the token expires. We display a visual badge showing whether your token is valid or expired based on the current time. We also show the iat (issued at) timestamp so you can see when the token was created.

JWT (JSON Web Token) is the umbrella term for tokens in this format. JWS (JSON Web Signature) refers to signed tokens where the content is visible but tamper-proof - this is what most people mean by "JWT". JWE (JSON Web Encryption) refers to encrypted tokens where the content is hidden. Most authentication tokens are JWS tokens, which this decoder handles perfectly. JWE tokens would need to be decrypted first with the encryption key.

Common reasons for JWT decoding errors include: 1) The token is incomplete or truncated - ensure you copied the entire token including all three parts (header.payload.signature). 2) The token has extra whitespace or newlines - paste only the token string. 3) It's not a valid JWT format - valid JWTs have exactly three parts separated by dots. 4) The token is encrypted (JWE) rather than signed (JWS) - encrypted tokens need decryption first. 5) Invalid Base64Url encoding - this usually indicates a corrupted or modified token.

Access tokens are short-lived JWTs (typically 15 minutes to 1 hour) used to access protected resources like APIs. They contain user claims and permissions. Refresh tokens are longer-lived tokens (days to weeks) used to obtain new access tokens without re-authentication. Refresh tokens are usually stored more securely and may or may not be JWTs. Our decoder can decode both types - just paste the token to see its contents and expiration.

This JWT decoder is perfect for debugging authentication issues: 1) Check if your token has expired (exp claim). 2) Verify the correct audience (aud) and issuer (iss) claims. 3) Inspect user roles and permissions in the payload. 4) Confirm the algorithm matches your server configuration. 5) Debug OAuth flows by comparing token contents. 6) Verify that required custom claims are present and correctly formatted.

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Why Use Our Free JWT Decoder?

Our online JWT decoder tool is trusted by thousands of developers for debugging and analyzing JSON Web Tokens. Here's why developers choose NoCostTools:

  • 100% Client-Side Processing - Your tokens never leave your browser, ensuring complete privacy and security
  • Instant Decoding - Real-time parsing as you type with immediate feedback
  • Syntax Highlighted Output - Beautiful JSON formatting with syntax highlighting for easy reading
  • Expiration Detection - Automatic detection and display of token validity status
  • All Algorithms Supported - Works with HS256, RS256, ES256, and all other JWT signing algorithms
  • No Registration Required - Use immediately without creating an account
  • Mobile Friendly - Works perfectly on smartphones and tablets
  • Free Forever - No hidden costs, premium tiers, or usage limits