IconVault's JWT Builder lets you create and inspect JSON Web Tokens without a server. Enter a header and payload as JSON, pick HS256, HS384 or HS512, add a secret, and the tool signs the token with WebCrypto HMAC in your browser. The result is decoded back into readable header and payload panels, and the signature is verified by re-signing, so you can see exactly what each part of the token contains.

Handy helpers include iat = now and exp = +1h timestamp buttons and a show/hide secret toggle, and you can copy the finished token with one click. Everything runs fully in your browser and it is free to try (heavy repeated use may ask for Pro). One hard rule: this tool is for testing only. Never paste production secrets or real user tokens here, and treat anything you paste as potentially visible.