mobiai-analyze-crash

Analyze Crash

Analyze a crash that the user provides, find the root cause in the codebase, and fix it.

When to Use

• User shares a stack trace, crash log, error screenshot, or any crash information
• User pastes a crash from any source (Crashlytics, Sentry, Bugsnag, logcat, Xcode console, a Slack message, an email — anything)
• User asks to investigate why something is crashing

What You Receive

The user may give you the crash in any format:

• A raw stack trace pasted into the chat
• A screenshot of a crash
• A log file
• A description like "the app crashes when I tap X"
• A URL to a crash reporting tool
• Anything else — work with what you have

Workflow

Step 1: Extract the Signal

From whatever the user gave you, identify the key information:

1. Exception / error type — e.g., NullPointerException, EXC_BAD_ACCESS, RangeError, SIGSEGV
2. Crash location — file, line number, method name (if available in the stack trace)
3. Call stack — the sequence of calls that led to the crash
4. Context — what the user was doing when it happened, which screen, which action

If the information is incomplete, ask the user for more context. But don't block on it — work with what you have.

Step 2: Classify the Crash Type

Identify the category to guide your investigation:

Type	Common Signals	Where to Look
Null reference	NullPointerException, EXC_BAD_ACCESS, forced unwrap nil	Trace where the null value originates — usually an upstream initialization issue
Concurrency	ConcurrentModificationException, data race, random EXC_BAD_ACCESS	Shared mutable state, missing synchronization, wrong thread
Index out of bounds	IndexOutOfBoundsException, ArrayIndexOutOfBoundsException	Array/list access without bounds checking, empty collections
Lifecycle	IllegalStateException, "view not attached", "no activity"	Fragment/Activity lifecycle, accessing UI after destroy
Memory	OutOfMemoryError, jetsam kill	Leaks, large bitmap allocations, unbounded caches
Network	SocketTimeoutException, SSLException	Missing error handling in network layer
Database	SQLiteException, Core Data error	Schema migrations, thread safety, constraint violations
Type casting	ClassCastException, Swift as! failure	Wrong type assumptions, generics, serialization

Step 3: Find the Root Cause in the Codebase

For root cause investigation, follow the mobiai-mobile-debugging skill methodology: no guessing, trace data backward, form hypotheses based on evidence.

Starting from the crash location:

1. Find the crashing code — use the file and line from the stack trace:

   Grep for the class name or method name from the stack trace
   Read the file at the crash location
   

2. Trace backwards — the crash site is usually not the root cause. Follow the data flow upstream:

   • Where does the null value come from?
   • Who populates this list that's empty?
   • What thread is calling this method?

3. Check recent changes — the crash may have been introduced recently:

   git log --oneline -10 -- <crashing-file>
   git blame <crashing-file>
   

4. Understand the full context — read surrounding code, the class structure, how the component is used.

Step 4: Decide — Fix or Propose

Based on confidence and complexity:

• High confidence, simple fix — apply the fix directly. Use the mobiai-fix-issue skill workflow: edit the code, verify it compiles, run tests.
• Complex fix or uncertain root cause — explain what you found, what the root cause is, and propose how to fix it. Let the user decide.
• Can't find the root cause — explain what you investigated, what you ruled out, and ask the user for more context.

Step 5: If Fixing

Apply a minimal fix:

• Change only what is necessary
• Do NOT refactor surrounding code
• Verify it compiles
• Run existing tests to check for regressions
• If applicable, load the mobiai-write-tests skill to add a regression test

Platform-Specific Patterns

Android

• FATAL EXCEPTION in logcat — app process crashed
• ANR (Application Not Responding) — main thread blocked >5 seconds
• Process: <package> lines identify which app crashed
• StrictMode violations in debug builds hint at production issues

iOS

• EXC_BAD_ACCESS — memory access violation (nil dereference, dangling pointer)
• EXC_BREAKPOINT — fatalError(), preconditionFailure(), Swift runtime checks
• Release builds need symbolication — atos or Xcode Organizer
• Crash reports in ~/Library/Logs/DiagnosticReports/

Flutter

• FlutterError — widget build errors, assertion failures
• Platform channel errors — bridge between Dart and native
• Check BOTH the Dart stack trace AND the native (Android/iOS) logs

React Native

• Red screen errors in development
• JavaScript errors in adb logcat | grep ReactNativeJS
• Native crashes appear in normal Android/iOS logs — not in JS

KMP

• Shared code crashes may appear differently per platform
• Check if the crash is in commonMain (shared) or platform-specific (androidMain/iosMain)
• Kotlin/Native memory model issues on iOS side