JWT.io

Yes — JWT.io does all decoding and signature verification entirely in client-side JavaScript. Open the browser DevTools Network tab while pasting a token and you'll see no outbound request. That said, best practice in security-sensitive environments is still to assume any web tool can be compromised; for high-stakes production tokens, prefer the offline jwt-cli, jwtinspector VS Code extension, or your language's native library.

Yes — JWT.io is fully free with no account required. It is operated by Okta (which acquired Auth0) as a developer-marketing site, alongside the jwt.io debugger libraries list and the JWT introduction articles. There is no paid tier; the cost to Okta is paid for via brand exposure to the auth developer community.

JWT.io is the browser-based reference debugger — fastest for ad-hoc inspection of a token someone pasted in Slack. jwt-cli is a Rust command-line tool that works offline, can be scripted in CI, and supports key files directly. For production debugging on shared infrastructure, jwt-cli is safer. For quick visual inspection during development, JWT.io is unbeatable. Most engineers use both.

Yes — JWT.io is a PWA that caches the full app on first visit, including the decoding/verification JavaScript bundle. After that, you can decode tokens and verify signatures (with a pasted key) entirely offline. The libraries-list page on jwt.io requires network, but the debugger does not.

JWT.io is bookmarked by essentially every developer working with OAuth 2.0, OIDC, or any Bearer-token API — Auth0, Okta, Firebase Auth, Supabase, Cognito, Azure AD users all land here when debugging an unexpected token shape. It is referenced in countless internal runbooks at companies of all sizes. The site reports tens of millions of annual visits, making it one of the most-used auth developer tools in existence.