JWT Toolkit — Free JWT Decoder, Validator & Inspector

JWT Toolkit is a free collection of twelve focused utilities for working with JSON Web Tokens. Every tool runs entirely in your browser: tokens, secrets and keys you paste here are never uploaded, never stored and never tracked.

JWT Tools Directory

Twelve free tools for decoding, inspecting, validating and analyzing JSON Web Tokens — all processed locally in your browser:

• JWT DecoderDecode JWT tokens to view header and payload
• JWT InspectorComprehensive analysis of JWT token structure and claims
• JWT Expiry CheckerCheck if JWT token is expired and view time remaining
• JWT Signature VerifierVerify JWT signature with secret or public key
• JWT Claims ViewerView all JWT claims in a tree-style format
• JWT Header ViewerDisplay JWT header information only
• JWT Payload FormatterPretty print JWT payload with proper indentation
• JWT Timestamp ConverterConvert JWT timestamps to readable dates
• JWT Lifetime CalculatorCalculate JWT token lifetime duration
• JWT Audience ValidatorValidate JWT audience claim against expected value
• JWT Secret Strength CheckerAnalyze JWT secret strength and security
• Base64URL DecoderDecode Base64URL encoded strings

What is JWT Toolkit?

JWT Toolkit is a complete developer suite for analyzing, decoding and validating JSON Web Tokens. It brings together twelve specialized tools — from a straightforward decoder to a signature verifier, expiry checker, timestamp converter and secret strength checker — behind one fast, consistent interface.

The toolkit is designed for everyday development work: debugging authentication flows, auditing tokens issued by your identity provider, verifying signatures while integrating an API, or simply learning how JWTs are structured. There is no registration, no account and no usage limit.

What is a JWT (JSON Web Token)?

A JSON Web Token (JWT) is an open standard (RFC 7519) for representing claims securely between two parties. A JWT is a compact, URL-safe string composed of three parts separated by dots: header.payload.signature.

Header

The header typically describes the token type (typ: "JWT") and the signing algorithm (alg), such as HS256 for HMAC-SHA256 or RS256 for RSA-SHA256. It is Base64URL-encoded JSON.

Payload

The payload carries the claims — statements about the subject and metadata. Registered claims include iss (issuer), sub (subject), aud (audience), exp (expiration time), nbf (not before), iat (issued at) and jti (JWT ID). Applications can also add custom claims. The payload is Base64URL-encoded, not encrypted.

Signature

The signature is created by signing the encoded header and payload with the algorithm named in the header — either a shared secret (HMAC) or a private key (RSA/ECDSA). It lets the recipient detect tampering and, with the right key, confirm the issuer.

Decoding vs. Signature Verification

Decoding a JWT only reverses the Base64URL encoding so you can read the header and payload. Anyone can decode any token — no key is required, and decoding proves nothing about authenticity.

Signature verification is the security step: the verifier recomputes the signature from the header and payload using the secret (for HMAC algorithms such as HS256/HS384/HS512) or the public key (for asymmetric algorithms such as RS256 or ES256) and compares it to the signature attached to the token. Only a matching signature shows the token was not modified. Never trust the contents of a token whose signature you have not verified.

JWT Security Considerations

JWTs are a building block, not a complete security solution. A few practices matter in almost every system that issues or consumes them:

• Always verify the signature and pin the expected algorithm — do not accept tokens that switch to alg "none" or a weaker algorithm.
• Validate exp, nbf, iss and aud on every request, and keep token lifetimes short.
• Use long, randomly generated secrets for HMAC signing; the JWT Secret Strength Checker can help you gauge entropy.
• Never place passwords or other sensitive data in the payload — it is only encoded, not encrypted.
• Transport tokens only over HTTPS and store them carefully on the client.

Local Browser Processing & Privacy

Every tool in JWT Toolkit executes locally in your browser using JavaScript and the Web Crypto API. Tokens and secrets you paste are processed on your device and are never transmitted to a server, written to a database or logged. There are no analytics on your input and no registration of any kind.

Because processing is client-side, the toolkit also works as a safe learning environment: you can inspect real tokens from your own applications without exposing them to a third party. As with any tool, avoid pasting production credentials on shared or untrusted computers.

Frequently Asked Questions

What is JWT?

JWT (JSON Web Token) is an open standard (RFC 7519) for securely transmitting information between parties as a JSON object. It consists of three parts: Header, Payload, and Signature, separated by dots.

How secure is JWT?

JWT security depends on proper implementation. When using strong secrets (for HMAC) or proper key management (for RSA/ECDSA), and when tokens are transmitted over HTTPS, JWTs are very secure. Always validate signatures and check expiration times.

What is HS256?

HS256 (HMAC with SHA-256) is a symmetric algorithm that uses a shared secret to sign and verify JWT tokens. Both the issuer and verifier must have the same secret key.

What is the exp claim?

The "exp" (expiration time) claim identifies the time after which the JWT must not be accepted. It is a NumericDate value representing seconds since Unix epoch (January 1, 1970).

What is the iat claim?

The "iat" (issued at) claim identifies the time at which the JWT was issued. It can be used to determine the age of the JWT and is represented as seconds since Unix epoch.

What is the audience claim?

The "aud" (audience) claim identifies the recipients that the JWT is intended for. Each principal intended to process the JWT must identify itself with a value in the audience claim.

Do you store my tokens?

No, absolutely not. All JWT processing happens entirely in your browser using JavaScript. Your tokens never leave your device, are never sent to our servers, and are never stored anywhere. Your data remains completely private.

What is the difference between HS256 and RS256?

HS256 uses a symmetric algorithm with a shared secret, while RS256 uses asymmetric RSA encryption with a private key for signing and a public key for verification. RS256 is more secure for distributed systems.

Can I use this tool for production tokens?

Yes, but be cautious. While all processing is local and private, avoid pasting production tokens on shared computers or in untrusted environments. For maximum security, use this tool only on your personal device.

What is the sub claim?

The "sub" (subject) claim identifies the principal that is the subject of the JWT. This is typically a user ID or username and must be unique within the issuer's context.

How long should a JWT secret be?

For HS256, use at least 256 bits (32 characters). For HS384, use at least 384 bits (48 characters). For HS512, use at least 512 bits (64 characters). Always use cryptographically random secrets.

What is the iss claim?

The "iss" (issuer) claim identifies the principal that issued the JWT. It is typically a URL or identifier of the authentication server that created the token.

Can JWT tokens be revoked?

JWTs are stateless and cannot be revoked by default. To implement revocation, you need to maintain a blacklist/denylist on the server side or use short expiration times with refresh tokens.

What is the nbf claim?

The "nbf" (not before) claim identifies the time before which the JWT must not be accepted for processing. It is useful for tokens that should only be valid after a certain time.

Should I include sensitive data in JWT?

No. JWT payloads are only Base64URL encoded, not encrypted. Anyone with the token can decode and read the payload. Never include passwords, credit card numbers, or other sensitive data.

What is Base64URL encoding?

Base64URL is a variant of Base64 encoding that is URL-safe. It replaces "+" with "-", "/" with "_", and removes padding "=" characters, making it safe to use in URLs and headers.

How do I verify a JWT signature?

Use our JWT Signature Verifier tool. Enter your token and the secret (for HMAC algorithms) or public key (for RSA/ECDSA). The tool will verify if the signature is valid and the token has not been tampered with.

What happens if a JWT expires?

An expired JWT should be rejected by the verifying party. The application should request a new token, typically using a refresh token mechanism, rather than accepting expired tokens.

Can I edit a JWT token?

You can decode and modify the payload, but any changes will invalidate the signature. To create a valid modified token, you need the secret key to generate a new signature.

Is this tool open source?

JWT Toolkit is built with modern open-source technologies including React, TailwindCSS, and the Web Crypto API. We are committed to transparency and security.

Do I need to install anything?

No installation required. JWT Toolkit runs entirely in your web browser. Just visit the website and start using the tools immediately.

What browsers are supported?

JWT Toolkit works on all modern browsers that support the Web Crypto API, including Chrome, Firefox, Safari, and Edge. We recommend using the latest version of your browser for the best experience.