JWT Decoder & Generator

100% Client-Side

Decode, verify, and generate JSON Web Tokens (JWT) instantly and securely in your web browser. Zero server transmission.

Supported Algorithms: HS256 HS384 HS512 RS256 RS512 ES256
Encoded JWT Token
Format: HEADER.PAYLOAD.SIGNATURE
HEADER: 0% (0 B) PAYLOAD: 0% (0 B) SIGNATURE: 0% (0 B)
Privacy Notice: Your JWT token remains in your browser and is never transmitted over the network.
Token Status:
HEADER: ALGORITHM & TOKEN TYPE
PAYLOAD: DATA CLAIMS
Token Expiry & Signature Validation
Signature Unchecked
JWT Generator Configuration
Quick Claims Injector
Generated Signed JWT
HEADER: 0% (0 B) PAYLOAD: 0% (0 B) SIGNATURE: 0% (0 B)
Error details...
Security Guarantee: JWT generation and signing happens 100% locally in your browser. Raw secrets or private keys are never transmitted.

JWT Decoder & Verifier — Debug and Validate JSON Web Tokens Online

Decode, parse, and verify JSON Web Tokens (JWT) locally and securely in your browser. Our online JWT Decoder supports verifying signatures natively using the standard browser Web Crypto API. You can debug HS256 symmetric HMAC secrets or RS256 asymmetric public keys in public PEM, JWK JSON, or X.509 certificate formats. The tool decodes JWT payload claims (such as exp, iat, and nbf) and evaluates token expiration with a real-time countdown timer. Since all cryptographic operations run fully client-side, your token data and private keys are never transmitted over the internet, keeping your credentials 100% safe.

How to Use the JWT Decoder & Verifier Tool:

  • Paste your encoded JSON Web Token (JWT) into the input box above.
  • The tool will instantly parse and color-highlight the token's Header and Payload.
  • View standard claims, verification status, and dynamic token expiry countdowns.
  • To verify the signature, select or input your cryptographic secret (HS256) or public key (RS256).
  • Copy or download decoded results locally as JSON or text format.

Frequently Asked Questions

Is my JWT token sent to a server?

Absolutely not. All JWT decoding, parsing, syntax coloring, and signature verification occur 100% locally in your web browser. No token data is ever uploaded or sent across the network.

How do I generate a secure JSON Web Token (JWT) online?

Simply switch to our JWT Encoder & Generator tab. Set your desired headers, payload claims, and sign with a symmetric secret (using our built-in 256-bit random secure key generator) or upload asymmetric PKCS#8 private keys. Signing runs entirely in the local sandbox via the Web Crypto API.

What is the difference between symmetric and asymmetric token signing?

Symmetric signing (HS256/384/512) uses a single shared secret key for both generating and verifying the token signature. Asymmetric signing (RS256, ES256) utilizes a keypair: the identity issuer signs the JWT with a private key (PKCS#8 PEM or JWK), and clients verify it using the public key.

What are the common JWT errors and what do they mean?
  • Invalid Signature: The token has been altered, or the secret/public key used for validation is incorrect.
  • Token Expired (exp): The current time is past the token's defined lifespan, meaning the token is no longer valid.
  • Malformed Token: The token does not consist of three dot-separated base64url segments.
  • Unsupported Algorithm: The algorithm header value in the token is not recognized or supported by the verifier.
  • JWE Warning: This is a 5-part encrypted JSON Web Encryption token instead of a 3-part signed token, requiring a decryption key.
Can this tool edit a JWT token?

This tool is designed primarily for parsing, syntax highlighting, and cryptographically validating existing tokens. Since editing a claim changes the payload content, it immediately invalidates the signature unless the token is re-signed with the correct private certificate key.

What is a JSON Web Token (JWT)?

JSON Web Token (JWT) is an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object. This information can be verified and trusted because it is digitally signed. JWTs can be signed using a secret (with the HMAC algorithm) or a public/private key pair using RSA or ECDSA.

JWT Anatomy & Structure

In its compact form, a JSON Web Token consists of three parts separated by dots (.), which are:

  • Header: Typically consists of two parts: the type of the token, which is JWT, and the signing algorithm being used, such as HS256, HS384, HS512, RS256, or ES256.
  • Payload: Contains the claims. Claims are statements about an entity (typically, the user) and additional data. There are three types of claims: registered, public, and private claims.
  • Signature: Created by hashing the encoded header, the encoded payload, and your secret key using the specified cryptographic signing algorithm.

Cryptographic Key Architectures: HS256 vs RS256

HS256 (HMAC with SHA-256) is a symmetric algorithm, meaning that a single secret key is shared and used by both the party creating the signature and the party verifying it. This makes verification extremely fast but requires sharing the secret.

RS256 (RSA Signature with SHA-256) is an asymmetric algorithm, which utilizes a public/private key pair. The identity provider signs the token with a private key, and the consumer verifies it using the matching public key, eliminating secret sharing risks.

Best Practices for JWT Security

  • Never store sensitive data in the payload: JWT content is Base64URL-encoded and can be trivially read by anyone. Never place passwords or credit card numbers in a claim.
  • Always validate algorithm headers: Prevent "alg: none" attacks by explicitly specifying the expected algorithm during server-side verification.
  • Enforce short Expiration Times (exp): Keep token lifespans short and use refresh tokens to mitigate token theft hazards.