Free JWT Decoder
Last updated: March 16, 2026
A JWT decoder parses JSON Web Tokens to reveal the header and payload data, including expiration status. Paste your JWT below to decode and inspect its contents instantly.
Decode JWT tokens to see header and payload. Expiration status, issued time & algorithm. Free online JWT decoder — no signup.
Software developers, DevOps engineers, and technical writers who need quick formatting and conversion utilities.
100% free, runs entirely in your browser — no signup, no data sent to any server.
How to Use the JWT Decoder Tool
JWT Decoder Features and Options
About the Free Online JWT Decoder
How to Decode JWT Tokens Online
1. Paste your JWT. Copy the full JWT string (three dot-separated parts) from your application, API response, browser dev tools, or authentication header and paste it into the input field.
2. View the decoded data. The header and payload appear as formatted JSON instantly. The Token Summary section shows the algorithm, type, issued time, and expiration status at a glance.
3. Check expiration. The expiration badge is color-coded: green means the token is still valid, yellow means it expires within one hour, and red means the token has already expired.
4. Copy the results. Use the Copy Header, Copy Payload, or Copy Full Decoded buttons to copy formatted JSON to your clipboard for use in documentation or debugging.
Understanding JSON Web Tokens in Web Development
JSON Web Tokens have become the dominant standard for authentication and authorization in modern web applications. Unlike traditional session-based authentication where the server stores session data, JWTs are stateless: all the information the server needs to authenticate a request is contained within the token itself. This makes JWTs ideal for distributed systems, microservices, and single-page applications.
How JWTs work is straightforward. When a user logs in, the server creates a JWT containing claims (user ID, roles, permissions) and signs it with a secret key. The client stores this token (usually in memory or an HTTP-only cookie) and sends it with every subsequent request. The server verifies the signature to ensure the token has not been tampered with, then reads the claims without needing to query a database.
Security considerations are critical when working with JWTs. The payload is only Base64URL-encoded, not encrypted, so anyone with the token can read its contents. Never store sensitive data like passwords or credit card numbers in a JWT. Always use HTTPS to prevent token interception. Set short expiration times and implement token refresh flows. Store tokens securely on the client side, ideally in HTTP-only, secure, SameSite cookies rather than localStorage.
Common JWT claims include 'sub' (subject, usually the user ID), 'iss' (issuer, who created the token), 'aud' (audience, who the token is intended for), 'exp' (expiration), 'iat' (issued at), and 'nbf' (not before). Applications can also include custom claims like roles, permissions, or tenant IDs. Keeping the payload small improves performance since the token is sent with every request.
Developers encounter JWTs daily when building APIs, debugging authentication issues, inspecting OAuth tokens, or integrating with identity providers like Auth0, Firebase Auth, or AWS Cognito. A quick decoder like this tool lets you inspect token contents without writing code, verify expiration times, and confirm that claims contain the expected values during development and troubleshooting.
Frequently Asked Questions About JWT Decoder
What is a JWT (JSON Web Token)?
A JWT is a compact, URL-safe token format used for securely transmitting information between parties as a JSON object. It consists of three Base64URL-encoded parts separated by dots: a header (algorithm and type), a payload (claims/data), and a signature. JWTs are commonly used for authentication, authorization, and information exchange in web applications.
Is it safe to decode JWTs in the browser?
Yes. The header and payload of a JWT are only Base64URL-encoded, not encrypted. Anyone with the token can decode and read them. The signature is what prevents tampering, not secrecy. This tool decodes the token locally in your browser — nothing is sent to any server. However, you should never paste tokens containing sensitive data into untrusted online tools.
What is the difference between decoding and verifying a JWT?
Decoding a JWT means reading the header and payload by Base64URL-decoding them. Anyone can do this. Verifying a JWT means checking that the signature is valid using the secret key (HMAC) or public key (RSA/ECDSA). Verification confirms the token hasn't been tampered with and was issued by a trusted party. This tool only decodes — it does not verify signatures.
What do iat, exp, and nbf mean in a JWT?
These are standard JWT claims. 'iat' (Issued At) is the Unix timestamp when the token was created. 'exp' (Expiration Time) is when the token expires and should no longer be accepted. 'nbf' (Not Before) is the earliest time the token should be accepted. All three are Unix timestamps (seconds since January 1, 1970 UTC).
What JWT algorithms are most common?
HS256 (HMAC with SHA-256) is the most common — it uses a shared secret key. RS256 (RSA with SHA-256) uses a public/private key pair and is preferred for distributed systems where you don't want to share the secret. ES256 (ECDSA with P-256) offers similar security to RS256 with smaller key sizes. PS256 (RSASSA-PSS) is a newer RSA variant with improved security properties.
Why does my JWT have three parts separated by dots?
The three parts are: (1) Header — contains the algorithm (alg) and token type (typ), Base64URL-encoded. (2) Payload — contains the claims (data), Base64URL-encoded. (3) Signature — created by signing the encoded header and payload with a secret or private key. The dots separate these three Base64URL-encoded strings.
Can an expired JWT be used?
An expired JWT should not be accepted by a properly implemented server. The 'exp' claim tells the server when to stop accepting the token. However, this is enforced by the server, not by the token itself. Some systems use refresh tokens to obtain new JWTs when the original expires, avoiding the need for the user to re-authenticate.
Is my data sent to a server?
No. All JWT decoding happens in your browser using JavaScript. Your token never leaves your device. The tool uses the built-in atob() function to decode Base64URL data locally.
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Decode JWTs here, then use our other developer tools for encoding, hashing, and data formatting.