Thing is, your local Diocese offers a website with parish details. Your local parish may have a website, a facebook page, etc. When people try to set up their own app, how do they get notified when Fr Joe has the flu and won’t be hearing confessions this week? Or when the schedule changes for the eleventy million reasons schedules change at a parish every week? Heck, often the parish office does not even know!
I often hear people recommed Mass Times website, I just checked it - they are a year behind on our mass schedule (meaning, our regular schedule changed a year ago and the old schedule is still there). There are also special changes, cancellations for this weekend, of course they are not listed.
It is always best to contact the parish and remember, not every parish has a staff to keep a website updated. Our Diocese no longer keeps mass times on the parish directories because keeping up with every parish and their changes is simply too much.