Crontab.guru is a genuinely good, minimal tool — a single box, instant human-readable translation, nothing else to load. If that's all you need, it's hard to beat and this page won't claim otherwise.
What this page adds: individual pages per common schedule (every 5 minutes, weekdays at 9am, and others) with a real-world use case for each, plus JSON/JWT/hash/regex tools in the same place if your task touches more than cron.