JSON Web Tokens (JWT) are an open RFC 7519 industry standard used for securely transmitting information between client applications and backend microservice servers. JWTs are widely used in modern authentication flows (OAuth 2.0, OpenID Connect) to pass user authorization state, session expiration, and role claims. Our Free Online JWT Decoder & Verifier allows backend engineers and security researchers to inspect Base64Url decoded claims in real time.
Equipped with real-time HMAC SHA-256 signature verification using your custom secret key, claim expiration analysis (`exp`, `iat`, `nbf`), and claim category badges, our tool provides full security insight into your authorization tokens. Everything operates 100% locally in your web browser using native Web Crypto APIs (`crypto.subtle`), ensuring that your authorization bearer tokens and private HMAC secret keys are never transmitted over the internet.
How to Decode & Verify JWT Tokens Online
Paste Encoded JWT String: Paste your raw JWT token (e.g. `eyJhbGci...`) into the left input panel.
Analyze Claims Breakdown: View automatic expiration status indicators and readable date-time translations for standard JWT timestamps.
Verify HMAC Signature: Enter your secret key in the Signature Verification box to perform real-time cryptographic validation.
Key Features & Technical Capabilities
Client-Side HMAC SHA-256 Verification: Verify token signatures locally using the browser's native Web Crypto API (`crypto.subtle`).
Automatic Expiration & Timestamp Conversion: Automatically converts Unix timestamps in `exp` (Expires At) and `iat` (Issued At) claims into readable dates.
Claims Breakdown & Role Analysis: Highlights core authentication parameters including subject, issuer (`iss`), audience (`aud`), and custom roles.
100% Private & Secure: Secrets and JWT access tokens never leave your web browser memory. Zero logging or network requests.
JWT Security Best Practices
Never Store Sensitive Data in Claims: JWT payloads are Base64Url encoded, NOT encrypted. Anyone with access to the token can read payload claims. Never store user passwords or credit card data inside a JWT payload.
Always Verify Token Signatures: Backend APIs must strictly verify token signatures before trusting payload claims to prevent spoofing.
Set Short Expiration Times: Use short access token lifetimes (e.g., 15 minutes to 1 hour) paired with secure refresh tokens to minimize hijack risks.
Frequently Asked Questions (FAQ)
Are my JWT access tokens or secret keys uploaded to any server?
No, absolutely not. All Base64Url decoding and HMAC signature verification execute 100% locally inside your web browser using native `crypto.subtle` APIs.
Is a JWT payload encrypted or just encoded?
JWT payloads are encoded using Base64Url, not encrypted. Anyone can decode and read the JSON payload. Cryptographic security comes from the digital signature, which prevents unauthorized tampering.
What happens when a JWT token expires (`exp`)?
When the current Unix timestamp exceeds the `exp` claim, backend server gateways will reject the token and demand authentication renewal.