Use when asked to debug, fix a bug, investigate an error, or do root cause analysis, and when users report errors, stack traces, unexpected behavior, or say something stopped working.
NO FIXES WITHOUT ROOT CAUSE INVESTIGATION FIRST.
Fixing symptoms creates whack-a-mole debugging. Every fix that doesn't address root cause makes the next bug harder to find. Find the root cause, then fix it.
Gather context before forming any hypothesis.
Collect symptoms: Read the error messages, stack traces, and reproduction steps. If the user hasn't provided enough context, ask ONE question at a time. Don't ask five questions at once.
Read the code: Trace the code path from the symptom back to potential causes. Search for all references, read the logic around the failure point.
Check recent changes:
git log --oneline -20 -- <affected-files>
Was this working before? What changed? A regression means the root cause is in the diff.
Reproduce: Can you trigger the bug deterministically? If not, gather more evidence before proceeding.
Check memory for prior debugging sessions on the same area. Recurring bugs in the same files are an architectural smell.
Output: "Root cause hypothesis: ..." ... a specific, testable claim about what is wrong and why.
Check if this bug matches a known pattern:
Race condition ... Intermittent, timing-dependent. Look at concurrent access to shared state.
Nil/null propagation ... NoMethodError, TypeError. Missing guards on optional values.
State corruption ... Inconsistent data, partial updates. Check transactions, callbacks, hooks.
Integration failure ... Timeout, unexpected response. External API calls, service boundaries.
Configuration drift ... Works locally, fails in staging/prod. Env vars, feature flags, DB state.
Stale cache ... Shows old data, fixes on cache clear. Redis, CDN, browser cache.
Also check:
External search: If the bug doesn't match a known pattern, search for the error type online. Sanitize first: strip hostnames, IPs, file paths, SQL, customer data. Search the error category, not the raw message.
Before writing ANY fix, verify your hypothesis.
Confirm the hypothesis: Add a temporary log statement, assertion, or debug output at the suspected root cause. Run the reproduction. Does the evidence match?
If the hypothesis is wrong: Search for the error (sanitize sensitive data first). Return to Phase 1. Gather more evidence. Do not guess.
3-strike rule: If 3 hypotheses fail, STOP. Tell the user:
"3 hypotheses tested, none match. This may be an architectural issue rather than a simple bug."
Options:
Red flags ... if you see any of these, slow down:
Once root cause is confirmed:
Fix the root cause, not the symptom. The smallest change that eliminates the actual problem.
Minimal diff: Fewest files touched, fewest lines changed. Resist the urge to refactor adjacent code.
Write a regression test that:
Run the full test suite. No regressions allowed.
If the fix touches >5 files: Flag the blast radius to the user before proceeding. That's large for a bug fix.
Fresh verification: Reproduce the original bug scenario and confirm it's fixed. This is not optional.
Run the test suite.
Output a structured debug report:
DEBUG REPORT
Save the report to memory/ with today's date so future sessions can reference it.