JWT Decoder

Decode JSON Web Tokens (JWT) client-side instantly. Split header, payload, and signatures, format JSON variables, and parse expiration times.

Enter Encoded JWT Token

Invalid Token: Make sure the JWT follows standard dot-separated formats containing three encoded segments.

Decoded Variables

HEADER: ALGORITHM & TOKEN TYPE

{ "alg": "HS256", "typ": "JWT" }

PAYLOAD: DATA / CLAIMS

{ "sub": "1234567890", "name": "AsheeshKG" }

SIGNATURE HASH SEGMENT

HMACSHA256(
  base64UrlEncode(header) + "." +
  base64UrlEncode(payload),
  YOUR_SECRET_KEY
)

What is a JSON Web Token (JWT)?

A **JSON Web Token (JWT)** is a compact, URL-safe data transfer standard used to represent claims between two parties. JWTs are widely implemented in secure microservices architectures, web authorization flows, and single-sign-on (SSO) systems. A token consists of three parts concatenated by dots `.`: a Header defining the signature algorithm, a Payload detailing session claims (like user IDs, email, and expirations), and a Signature verification hash. Decoding tokens helps backend developers debug permission rules, review payload keys, and track expired sessions.

All decryption and decoding steps occur locally on your computer. The token is never shared over server channels, preventing key exposures.

Frequently Asked Questions (FAQ)

Is decoding a JWT safe?

Yes, because JWTs are only **signed and base64 encoded**, not encrypted. Anyone who intercepts a token can read its header and payload claims easily. Therefore, you should never store sensitive personal details, passwords, or database credentials inside the payload block of a JWT.

What does this tool's expiration countdown track?

The token's payload contains standard parameters: `iat` (issued at time) and `exp` (expiration time) in Unix epoch formats. This tool parses these variables, translates them into human-readable date strings matching your local timezone, and runs an active ticking countdown to display how much time is left before authorization breaks.

Why does the signature block say "HMACSHA256"?

The header block lists the algorithm used to sign the token. Common options include symmetric HMAC-SHA256 or asymmetric RSA algorithms. Since verification requires the secret key, this offline tool displays signature structure instructions without trying to authenticate the token locally.