How it's measured
- Crash-free sessions: percentage of sessions without a crash.
- Crash-free users: percentage of users who had no crash in a period.
Tools such as Firebase Crashlytics report both. Google Play's Android vitals also track a "user-perceived crash rate", and Google says apps above its bad-behavior thresholds can get less visibility in the Play Store.
Why it matters
Crashes are the fastest way to lose users and stars. A crash on launch after an update typically shows up as a burst of one-star reviews within hours — often before the crash dashboard makes it obvious, because users also describe what they were doing.
How to protect yourself
- Roll out gradually with a phased release (iOS) or staged rollout (Android) and watch crashes and reviews.
- Alert on crash spikes and on new low-rating reviews — e.g. with app review monitoring.
- Reply to affected users with a developer response once the fix ships.
Example
Version 6.1 has a 99.9% crash-free rate on most devices but crashes on launch on one older Android version. Three one-star reviews mentioning that phone arrive in the first hour of the staged rollout; the team halts the rollout at 5%.