Systematic Debugging Strategy

Initial Assessment

Before diving in, gather context:

1. What changed? - Recent code changes, deployments, dependencies
2. When did it start? - Timeline helps narrow scope
3. Reproducible? - Consistent vs intermittent affects approach
4. Error messages? - Exact text, stack traces, logs
5. Environment? - Dev/staging/prod, OS, versions

Debugging Hierarchy (Work Through In Order)

1. Read the Error Message

• Parse the FULL stack trace
• Note the originating file and line number
• Look for "Caused by" chains
• Search error message verbatim if unclear

2. Reproduce Locally

• Create minimal reproduction case
• Isolate variables (data, environment, timing)
• Add logging at key points

3. Binary Search the Problem

• Comment out half the code
• Does it still fail? Problem is in remaining half
• Repeat until isolated

4. Check the Obvious

• Is it saved? Is it deployed?
• Correct environment variables?
• Dependencies installed/updated?
• Cache cleared?
• Correct branch?

5. Trace Data Flow

• Log inputs at entry point
• Log outputs at each transformation
• Find where actual diverges from expected

Common Bug Patterns

Symptom	Likely Causes
Works locally, fails in prod	Env vars, paths, permissions, CORS
Intermittent failure	Race condition, caching, timing
Undefined/null error	Missing data, async timing, typo
Silent failure	Swallowed exception, wrong error handler
Performance degradation	N+1 queries, memory leak, missing index

Debug Tools by Domain

JavaScript/React:

• Browser DevTools (Console, Network, React DevTools)
• console.log, console.table, debugger
• React Query DevTools, Redux DevTools

React Native:

• Flipper, React Native Debugger
• adb logcat (Android), Console.app (iOS)
• Remote JS debugging

Node.js:

• --inspect flag + Chrome DevTools
• DEBUG=* environment variable
• node --trace-warnings

Database:

• Query explain plans
• Slow query logs
• Connection pool monitoring

Output Format

When reporting findings:

1. Root Cause - What actually caused the bug
2. Fix - Code change required
3. Prevention - How to avoid similar bugs
4. Testing - How to verify the fix