Root-causing defects instead of guessing: reproduce, isolate, instrument component boundaries, kill hypotheses, and recognise when to question the design. Use on any bug, flaky test, or unexplained behaviour.
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What the file says
# Systematic debugging
Debugging is hypothesis testing against a running system, not code reading followed by a guess.
## Phase 1: Reproduce
- Get a reliable, minimal reproduction: exact command, input, environment.
- Confirm you can make it fail on demand. Cannot reproduce it? Say so, collect frequency and conditions before theorising.
- Capture the failure itself: full error text, stack, exit code. Not a paraphrase.
## Phase 2: Isolate
- Shrink the reproduction until the smallest failing unit is visible (scope, input size, config).
- Binary-search the surface: return early or disable at the midpoint of the suspect path. The failure is on one side of the cut; halve again.
- Instrument component boundaries. At each boundary, log what goes IN and what comes OUT. Find the FIRST boundary whose output is wrong given a correct input. The fault lives between the last correct boundary and that one.
- Let the system tell you where it breaks. You do not need to read all the code.
## Phase 3: Fix the cause, or question the design
- **Fixed-cause**: you can say why it broke and why the fix prevents exactly that. **Guessed-cause** ("this might help") is not done.
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The line at the top of this page pins the label git:20261010.ee06e2b, which is what most people want. This one pins the sha256 fingerprint of the contents instead, so it survives a label being moved. Either way the exact version is written to mdr.lock, and mdr install downloads and checks those contents again, so it installs them exactly or stops with an error.
GET https://markdownregistry.com/api/v1/artifacts/art_csbfybls5dgu3kmn
GET https://markdownregistry.com/api/v1/resolve?ref=damianvtran/local-operator/systematic-debugging
GET https://markdownregistry.com/api/v1/blob/ae7dea2d1c2353ae0ac90b63201b72e6a4dd6a8dd0f11381d94e88b078486ad6
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