JWT Decoder
Decode and inspect JSON Web Token headers and payloads. Shows expiry status and remaining time instantly. 100% client-side.
⚠ Signature verification requires the secret key and is not performed client-side.
About This Tool
The DevKit4You JWT Decoder is a secure, browser-based tool for decoding and inspecting JSON Web Tokens (JWTs) instantly. It helps developers analyze JWT headers, payloads, expiration timestamps, and token metadata without sending any data to external servers.
JWTs are widely used in authentication systems, APIs, OAuth flows, and modern web applications. This tool makes it easy to understand token contents during development, debugging, testing, and API integration workflows. The decoder is completely client-side — your token never leaves your browser.
How to Use
Copy and paste your JWT into the input field. A JWT has three dot-separated sections — if it doesn't, you'll see a format error immediately.
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9
.eyJzdWIiOiJ1c2VyXzQyIiwibmFtZSI6IkpvaG4gRG9lIiwiZXhwIjo5OTk5OTk5OTk5fQ
.SflKxwRJSMeKKF2QT4fwpMeJf36POk6yJV_adQssw5c
The decoded Header shows the signing algorithm (alg) and token type (typ). The decoded Payload shows all claims — standard ones like sub, iat, exp, and any custom claims added by the issuer.
If the token has an exp claim, the tool automatically shows whether the token is still valid and how much time remains, or when it expired. Use the Copy buttons to copy the Header or Payload JSON for debugging.
JWT Structure Explained
A JSON Web Token consists of three Base64URL-encoded parts joined by dots:
header.payload.signature
| Part | Content | Example Claims |
|---|---|---|
| Header | Algorithm & token type | alg, typ, kid |
| Payload | Claims about the entity | sub, iat, exp, iss, aud, custom claims |
| Signature | HMAC / RSA / ECDSA of header + payload | Requires secret or public key to verify |
The Header and Payload are Base64URL-encoded JSON — anyone can read them. The Signature is what makes a JWT tamper-proof: it can only be verified by the party that holds the secret or public key.
Standard JWT Claims Reference
| Claim | Full Name | Description |
|---|---|---|
| sub | Subject | Unique identifier of the user or entity the token represents |
| iss | Issuer | The server or service that issued the token (e.g. auth.example.com) |
| aud | Audience | The intended recipient(s) of the token |
| iat | Issued At | Unix timestamp of when the token was created |
| exp | Expiration | Unix timestamp after which the token must not be accepted |
| nbf | Not Before | Unix timestamp before which the token must not be accepted |
| jti | JWT ID | Unique identifier for the token — used to prevent replay attacks |
Key Capabilities
Automatically reads the exp claim and compares it to the current time. Shows remaining validity (e.g. "expires in 2h 14m") or an expired warning with the exact timestamp.
Displays the signing algorithm from the alg header field — HS256, RS256, ES256, PS256, and others. Helps identify whether the token uses symmetric or asymmetric signing.
Both the Header and Payload are displayed as indented, formatted JSON — making it easy to scan claims without manually decoding Base64URL strings.
The tool does not sign, verify, or modify tokens. It cannot validate the signature without the secret or public key — and it doesn't try. This makes it safe to use with real tokens during development.
Privacy & Security
JWT decoding happens entirely on your device using local browser processing. Your token — including any user claims, roles, or session data it contains — is never transmitted to any server.
We do not collect, save, or transmit JWT tokens, payload data, user claims, or authentication information. Nothing is retained after you close the page.
For security reasons, the tool does not attempt to verify signatures. Signature verification requires a secret key or public key and a trusted issuer — none of which are available or appropriate in a client-side tool. The decoder is strictly a read-only inspection utility.
🔒 Safe & Secure
All JWT decoding runs locally in your browser. Your tokens — including access tokens, identity tokens, and session JWTs — never leave your device. Safe to use during active development and debugging.
✅ Completely Free
Our tool is free to use with no limits, no watermarks, and no signup. Open the page, paste your token, and decode immediately — always free, always private.