Both decode header and payload claims identically — this is a solved problem, neither tool has an edge here.
JWT.io can verify a signature if you paste in the secret or public key. This tool doesn't offer that at all — see /jwt-validator for exactly what it checks instead (structure and expiration, not cryptographic validity).
JWT.io can construct a new signed token from scratch. This tool can't — it's decode-only.
JWT.io is owned by Auth0 (an Okta company). This tool isn't affiliated with any auth vendor, which matters to some teams with policies against inspecting tokens in a vendor-owned tool.
This tool sits alongside regex, JSON, cron, and hash tools in one app. JWT.io is JWT-only, with links out to language-specific libraries.