Keeping Crash-Free Sessions > 99 %: Our Playbook with Crashlytics + Sentry

A single crash can nudge a five-star app to four-point-something—and bump you down the App Store or Google Play rankings. At THE USEFUL APPS we treat stability as a feature; every client retainer includes a guarantee that crash-free sessions stay above 99 %.

Below you'll find the exact monitoring, triage, and release loop we've refined while maintaining apps like RouteMate and PHNews. Pairing Firebase Crashlytics (for mobile-first signal) with Sentry (for full-stack visibility) gives us near-real-time insight without drowning our devs in alert fatigue.

Table of Contents

1. Why 99 % Isn't Just a Vanity Metric
2. Our Two-Layer Monitoring Toolkit
3. Instrumentation Checklist (iOS, Android & Flutter)
4. Alert Routing: Noise ⟶ Signal
5. Release Annotation & Regression Hunting
6. Hot-Patch Workflow (24-Hour Fix Pledge)
7. Maintenance Retainer Tie-In
8. Sentry vs. Crashlytics: Which Handles What?
9. Security & PII Considerations
10. Key Metrics We Track
11. Conclusion

TL;DR

1. Instrument everything (Crashlytics SDK + Sentry mobile & back-end SDKs).
2. Route alerts through a single Slack channel with severity filters.
3. Annotate releases so we can bisect instantly.
4. Hot-patch critical issues via feature flags; ship store updates within 24 h.
5. Close the loop by feeding crash metrics into sprint retros.

1. Why 99 % Isn't Just a Vanity Metric

Google's internal research shows a direct correlation between crash rate and uninstalls , while Apple's ranking algorithm quietly penalises apps with high "User Terminated" signals. Falling from 99 % to 97 % sounds minor—but if you have 100 k daily sessions, that's 2 000 crashes per day.

Keeping the number above 99 %:

• Protects your App Store rating
• Reduces churn (RouteMate saw a 3 % retention lift after we fixed a background-fetch crash)
• Boosts conversion in paid campaigns (nobody installs a 3.8-star app)

2. Our Two-Layer Monitoring Toolkit

Crashlytics handles native stack traces across Swift, Kotlin, Flutter, and React Native. Sentry handles our Node, Python, or Go back-ends plus any React in webviews. Together, they give us a single view from tap to database write.

3. Instrumentation Checklist (iOS, Android & Flutter)

We commit a monitoring.md file in every repo documenting SDK versions, manual uploads, and DSNs. That doc lives next to the CI config so future engineers see the full picture.

4. Alert Routing: Noise ⟶ Signal

Raw Crashlytics alerts = chaos. We pipe both Crashlytics and Sentry through AWS SNS ➔ Slack with opinionated filters:

1. Blocklisted: Known-benign Tesla BLE failure? Ignore.
2. Critical: New crash > 0.1 % sessions within one hour -> page engineer on duty.
3. Moderate: New crash group with < 0.1 % sessions -> Slack thread.

This reduces false positives by ~70 % compared to default email alerts.

5. Release Annotation & Regression Hunting

In both tools we tag every CI build with:

• Git SHA
• Semantic app version
• Feature flag bundle
• Jira sprint ID

Crashlytics then shows "First seen in 2.13.0 (Build #231)" so PMs can bisect instantly. Sentry's Release Health dashboard tracks crash-free sessions per build , highlighting regressions we might have missed.

6. Hot-Patch Workflow (24-Hour Fix Pledge)

When a critical crash surfaces:

Our RouteMate engagement once hit a nasty SIGABRT in iOS 17 RC. Flag rollback cut crashes to zero in 90 minutes; the store patch landed next day.

7. Maintenance Retainer Tie-In

This process lives inside every Maintenance & Support plan. Clients know exactly what happens when a spike appears—no awkward "scope" arguments. For details on the tiers, read App Maintenance Strategies for Long-Term Success.

8. Sentry vs. Crashlytics: Which Handles What?

We keep both, but if you only have budget for one and your stack is 100 % Flutter, Crashlytics alone covers 95 % of pain points.

9. Security & PII Considerations

• Use Crashlytics data redaction rules to strip email/phone from logs.
• In Sentry, set sendDefaultPii = false and add beforeSend hook.
• Ensure DSNs and Google Service Plist files are stored as GitHub Secrets.
• SOC 2 clients often require 90-day log retention; both tools support that.

10. Key Metrics We Track

We pull these into a Monday morning Looker Studio report for each client.

Conclusion

Maintaining > 99 % crash-free sessions isn't magic—it's disciplined instrumentation, fast feedback loops, and the willingness to hot-patch at 3 a.m. Using Crashlytics for native signal and Sentry for end-to-end context, we've helped brands like Skip hold five-star ratings year after year.

Want this playbook applied to your app? Reach out or explore the specifics of our Care, Growth & Scale plans—each one includes the 24-hour fix pledge.