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Debugging-First Round

Forward Deployed Engineering

What it tests

Diagnostic thinking — can they find and fix bugs in unfamiliar code?

Format

  1. 1Give candidate a broken application (your product or a simplified version)
  2. 23-5 bugs of increasing difficulty: syntax error, logic error, race condition, performance issue (N+1 query), subtle security vulnerability
  3. 3Candidate debugs live, explaining their thought process

What to look for

  • Systematic debugging (vs. random guessing)
  • Tool usage (debugger, logging, profiling)
  • How they explain their reasoning (critical for customer-facing eng)
  • Do they find the root cause or just patch the symptom?

Full description

Format:

  1. Give candidate a broken application (your product or a simplified version)
  2. 3-5 bugs of increasing difficulty:
    • Bug 1: Syntax error (warm-up)
    • Bug 2: Logic error in data transformation
    • Bug 3: Race condition in async code
    • Bug 4: Performance issue (N+1 query, memory leak)
    • Bug 5: Subtle security vulnerability
  3. Candidate debugs live, explaining their thought process

Time: 60 minutes

What to look for:

  • Systematic debugging (vs. random guessing)
  • Tool usage (debugger, logging, profiling)
  • How they explain their reasoning (critical for customer-facing eng)
  • Do they find the root cause or just patch the symptom?

Why debugging > building: FDE/SE work is 70% debugging customer issues, 30% building new features. Testing what they'll actually do on the job.