JWT Decoder
Decode and inspect JSON Web Token claims instantly in your browser. Free and private — your token never leaves your device. No account needed.
JWT Decoder
Decode completely client-side. No tokens are sent to our servers.
Encoded Token string
HEADER Algorithm & Token Type
PAYLOAD Data / Claims
SIGNATURE
What is a JWT?
A JWT (JSON Web Token) is a compact, self-contained token format used for authentication and authorization. It consists of three Base64-encoded parts separated by dots — header.payload.signature. The header describes the signing algorithm, the payload contains claims like user ID and expiry time, and the signature verifies the token has not been tampered with.
JWTs are stateless — the server does not need to store session data. Instead, all the information needed to authorize a request is encoded directly in the token. Each request includes the JWT, and the server verifies it by checking the signature against its secret key.
How to Use the JWT Decoder
Paste your JWT
Paste the JWT string into the input field. It should be three dot-separated Base64 strings: header.payload.signature.
Inspect the decoded output
The tool instantly decodes and displays the header and payload as formatted JSON. Review user ID, roles, expiry (exp), issued-at (iat), and custom claims.
Check expiry and timestamps
The exp and iat fields are Unix timestamps. The tool converts them to human-readable dates so you can see when the token was issued and when it expires.
Debug or document
Use the decoded output to debug authentication flows, verify claim structure, or document what your API tokens expose for security reviews.
The Anatomy of a JWT
A JWT is a string consisting of three parts separated by dots (.):
- 1. Header Contains the cryptographic algorithm used to secure the token (e.g., HMAC SHA256 or RSA) and the type of token (JWT).
- 2. Payload
Contains the "claims" — statements about an entity (typically, the user) and additional data like the token's expiration date (
exp). They are readable by anyone, so highly confidential information should never go here. - 3. Signature Created by hashing the encoded header, the encoded payload, and a secret server-side key. The signature ensures the token has not been tampered with in transit.
Who Is This For?
- ▸ Developers debugging authentication flows who want to inspect what claims a JWT contains without writing a script to decode it manually.
- ▸ Backend engineers verifying token structure during API development — confirm the payload contains the expected fields before shipping an auth endpoint.
- ▸ Security reviewers auditing what data a token exposes — verify that sensitive information like passwords or PII is not accidentally included in the JWT payload.
Key Benefits
- ✓ Runs entirely in your browser — your token is never transmitted to or stored on a server.
- ✓ Free with no subscription — no account, no paywall, no usage limits.
- ✓ No account required — open the page and start decoding immediately.
- ✓ Human-readable timestamps — Unix timestamps in exp and iat fields are automatically converted to readable dates.
Common Use Cases
A user reports they are being logged out unexpectedly. Decode the JWT from the browser's local storage to check the exp claim and confirm whether the token is expiring sooner than expected.
You are integrating a third-party authentication provider and need to confirm which claims are included in the token — user ID, email, roles, and tenant ID. Paste the token and inspect the payload to map each field before writing your authorization logic.
You are doing a security review and need to verify that the JWT payload does not expose sensitive data. Decode several tokens from your staging environment and confirm no PII or credentials are included in the claims.
Frequently Asked Questions
What is a JWT?
A JWT (JSON Web Token) is a compact, self-contained token format used for authentication and authorization. It consists of three Base64-encoded parts separated by dots — header.payload.signature. The header describes the signing algorithm, the payload contains claims like user ID and expiry time, and the signature verifies the token has not been tampered with.
Is this tool free?
Yes — completely free with no account required. The JWT decoder runs entirely in your browser. Your token is never sent to a server — all decoding is done locally using JavaScript.
Is it safe to decode a JWT in the browser?
Decoding — reading the payload — is always safe to do. A JWT's payload is not encrypted, only Base64-encoded, so the contents are readable by anyone who has the token. This tool runs entirely in your browser and your token never leaves your device. That said, never paste a production token from a high-security system into an online tool you do not trust.
What is the difference between JWT and session cookies?
JWT is stateless — the server does not need to store anything; all the information is contained in the token itself. Session cookies require server-side session storage — the server stores session data and the cookie just holds a session ID. JWT is common in APIs and microservices. Session cookies are more common in traditional server-rendered web applications.
Does decoding a JWT validate its signature?
No. Decoding only translates the Base64-encoded string back into readable JSON — it does not verify authenticity. Verifying the signature requires the private secret key, which is kept on your authentication server. This tool shows you what the token contains; it cannot tell you whether the token is valid or authentic.
Is it safe to paste my production JWT here?
Yes. The Simple Toolbox JWT Decoder runs 100% locally in your browser. Your token is never transmitted over a network, recorded, or saved to a server database. This tool was built specifically for developers with strict compliance and data security requirements.
The tools and calculators provided on The Simple Toolbox are intended for educational and informational purposes only. They do not constitute financial, legal, tax, or professional advice. While we strive to keep calculations accurate, numbers are based on user inputs and standard assumptions that may not apply to your specific situation. Always consult with a certified professional (such as a CPA, financial advisor, or attorney) before making significant financial or business decisions.
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