JWT Encoder & Decoder
Encode payloads into real HMAC-SHA256 signed JWTs, or decode and verify any JWT token. Runs entirely in your browser — nothing is sent to any server.
{"alg":"HS256","typ":"JWT"}. Signature uses HMAC-SHA256 via the browser's native Web Crypto API. About JWT (JSON Web Tokens)
JSON Web Tokens (JWT) are an open standard (RFC 7519) format for securely transmitting information as a JSON object. Tokens are digitally signed using a cryptographic secret (HMAC-SHA256) or public/private key pair.
Our online JWT Encoder & Decoder utilizes the browser's native Web Crypto API to decode base64url-encoded headers and claims, check expiration timestamps (exp), and generate HMAC-SHA256 signatures client-side. Your secrets and session tokens never leave your browser.
Real-World Use Cases
🔑 API Authorization Debugging
Inspect Bearer tokens returned by OAuth2 / OpenID Connect identity providers (e.g. Auth0, Firebase, Keycloak) to check roles, permissions, and expiration.
🧪 Backend Integration Testing
Generate custom signed JWT tokens with test claims and secrets to test REST API endpoints or microservices without deploying auth services.
⏰ Expiration & Refresh Verification
Check whether an expired auth token caused API 401 Unauthorized errors by inspecting the exp claim against current UTC timestamps.
Frequently Asked Questions
What is a JWT?
A JSON Web Token (JWT) is a URL-safe token format consisting of three base64url-encoded segments separated by dots: header.payload.signature.
Is my secret key safe when testing here?
Yes. All signature generation and validation occurs locally in your web browser using WebCrypto. No tokens or secrets are uploaded to external servers.
What algorithm does this tool support?
This tool supports HS256 (HMAC-SHA256), the standard symmetric signing algorithm used across REST APIs and web apps.