JWT.io does two things this tool doesn't: it can verify a signature if you paste in the secret or public key, and it can encode a new token from scratch. If you need either of those, JWT.io is the right tool — this page won't pretend otherwise.
What this page offers instead: decoding and claims inspection with the same result, without leaving the rest of your dev-tools workflow (JSON, cron, hash, regex all live here too), and without it being a vendor-affiliated tool — JWT.io is owned by Auth0/Okta, and some teams have policies against inspecting tokens in a competitor-owned or vendor-owned tool regardless of how the processing actually works.
Need to verify a signature or construct a token: use JWT.io. Just need to see what's inside a token, or want it alongside your other dev tools: this page.