diagnosing-bugs

Name: diagnosing-bugs
Author: tt-a1i

16stars3forks

How to install diagnosing-bugs?

tt-a1i/matt-skills-with-to-goal/diagnosing-bugs

$npx -y skills add tt-a1i/matt-skills-with-to-goal --skill diagnosing-bugs

Installs into the current project.

Summary

Diagnosis loop for hard bugs and performance regressions. Use when the user says "diagnose"/"debug this", or reports something broken/throwing/failing/slow.

Files · 1

View on GitHub

SKILL.md

1	# Diagnosing Bugs
2
3	A discipline for hard bugs. Skip phases only when explicitly justified.
4
5	When exploring the codebase, read `CONTEXT.md` (if it exists) to get a clear mental model of the relevant modules, and check ADRs in the area you're touching.
6
7	## Phase 1 — Build a feedback loop
8
9	This is the skill. Everything else is mechanical. If you have a tight pass/fail signal for the bug — one that goes red on _this_ bug — you will find the cause; bisection, hypothesis-testing, and instrumentation all just consume it. If you don't have one, no amount of staring at code will save you.
10
11	Spend disproportionate effort here. Be aggressive. Be creative. Refuse to give up.
12
13	### Ways to construct one — try them in roughly this order
14
15	1. Failing test at whatever seam reaches the bug — unit, integration, e2e.
16	2. Curl / HTTP script against a running dev server.
17	3. CLI invocation with a fixture input, diffing stdout against a known-good snapshot.
18	4. Headless browser script (Playwright / Puppeteer) — drives the UI, asserts on DOM/console/network.
19	5. Replay a captured trace. Save a real network request / payload / event log to disk; replay it through the code path in isolation.
20	6. Throwaway harness. Spin up a minimal subset of the system (one service, mocked deps) that exercises the bug code path with a single function call.
21	7. Property / fuzz loop. If the bug is "sometimes wrong output", run 1000 random inputs and look for the failure mode.
22	8. Bisection harness. If the bug appeared between two known states (commit, dataset, version), automate "boot at state X, check, repeat" so you can `git bisect run` it.
23	9. Differential loop. Run the same input through old-version vs new-version (or two configs) and diff outputs.
24	10. HITL bash script. Last resort. If a human must click, drive _them_ with `scripts/hitl-loop.template.sh` so the loop is still structured. Captured output feeds back to you.
25
26	Build the right feedback loop, and the bug is 90% fixed.
27
28	### Tighten the loop
29
30	Treat the loop as a product. Once you have _a_ loop, tighten it:
31
32	- Can I make it faster? (Cache setup, skip unrelated init, narrow the test scope.)
33	- Can I make the signal sharper? (Assert on the specific symptom, not "didn't crash".)
34	- Can I make it more deterministic? (Pin time, seed RNG, isolate filesystem, freeze network.)
35
36	A 30-second flaky loop is barely better than no loop; a 2-second deterministic one is tight — a debugging superpower.
37
38	### Non-deterministic bugs
39
40	The goal is not a clean repro but a higher reproduction rate. Loop the trigger 100×, parallelise, add stress, narrow timing windows, inject sleeps. A 50%-flake bug is debuggable; 1% is not — keep raising the rate until it's debuggable.
41
42	### When you genuinely cannot build a loop
43
44	Stop and say so explicitly. List what you tried. Ask the user for: (a) access to whatever environment reproduces it, (b) a captured artifact (HAR file, log dump, core dump, screen recording with timestamps), or (c) permission to add temporary production instrumentation. Do not proceed to hypothesise without a loop.
45
46	### Completion criterion — a tight loop that goes red
47
48	Phase 1 is done when the loop is tight and red-capable: you can name one command — a script path, a test invocation, a curl — that you have already run at least once (paste the invocation and its output), and that is:
49
50	- [ ] Red-capable — it drives the actual bug code path and asserts the user's exact symptom, so it can go red on this bug and green once fixed. Not "runs without erroring" — it must be able to _catch this specific bug_.
51	- [ ] Deterministic — same verdict every run (flaky bugs: a pinned, high reproduction rate, per above).
52	- [ ] Fast — seconds, not minutes.
53	- [ ] Agent-runnable — you can run it unattended; a human in the loop only via `scripts/hitl-loop.template.sh`.
54
55	If you catch yourself reading code to build a theory before this command exists, stop — jumping straight to a hypothesis is the exact failure this skill prevents. No red-capable command, no Phase 2.
56
57	## Phase 2 — Reproduce + minimise
58
59	Run the loop. Watch it go red — the bug appears.
60
61	Confirm:
62
63	- [ ] The loop produces the failure mode the user described — not a different failure that happens to be nearby. Wrong bug = wrong fix.
64	- [ ] The failure is reproducible across multiple runs (or, for non-deterministic bugs, reproducible at a high enough rate to debug against).
65	- [ ] You have captured the exact symptom (error message, wrong output, slow timing) so later phases can verify the fix actually addresses it.
66
67	### Minimise
68
69	Once it's red, shrink the repro to the smallest scenario that still goes red. Cut inputs, callers, config, data, and steps one at a time, re-run

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diagnosing-bugs

16stars3forks

View on GitHub

How to install diagnosing-bugs?

tt-a1i/matt-skills-with-to-goal/diagnosing-bugs

$npx -y skills add tt-a1i/matt-skills-with-to-goal --skill diagnosing-bugs

Installs into the current project.

Summary

Diagnosis loop for hard bugs and performance regressions. Use when the user says "diagnose"/"debug this", or reports something broken/throwing/failing/slow.

Files · 1

View on GitHub

SKILL.md

1	# Diagnosing Bugs
2
3	A discipline for hard bugs. Skip phases only when explicitly justified.
4
5	When exploring the codebase, read `CONTEXT.md` (if it exists) to get a clear mental model of the relevant modules, and check ADRs in the area you're touching.
6
7	## Phase 1 — Build a feedback loop
8
9	This is the skill. Everything else is mechanical. If you have a tight pass/fail signal for the bug — one that goes red on _this_ bug — you will find the cause; bisection, hypothesis-testing, and instrumentation all just consume it. If you don't have one, no amount of staring at code will save you.
10
11	Spend disproportionate effort here. Be aggressive. Be creative. Refuse to give up.
12
13	### Ways to construct one — try them in roughly this order
14
15	1. Failing test at whatever seam reaches the bug — unit, integration, e2e.
16	2. Curl / HTTP script against a running dev server.
17	3. CLI invocation with a fixture input, diffing stdout against a known-good snapshot.
18	4. Headless browser script (Playwright / Puppeteer) — drives the UI, asserts on DOM/console/network.
19	5. Replay a captured trace. Save a real network request / payload / event log to disk; replay it through the code path in isolation.
20	6. Throwaway harness. Spin up a minimal subset of the system (one service, mocked deps) that exercises the bug code path with a single function call.
21	7. Property / fuzz loop. If the bug is "sometimes wrong output", run 1000 random inputs and look for the failure mode.
22	8. Bisection harness. If the bug appeared between two known states (commit, dataset, version), automate "boot at state X, check, repeat" so you can `git bisect run` it.
23	9. Differential loop. Run the same input through old-version vs new-version (or two configs) and diff outputs.
24	10. HITL bash script. Last resort. If a human must click, drive _them_ with `scripts/hitl-loop.template.sh` so the loop is still structured. Captured output feeds back to you.
25
26	Build the right feedback loop, and the bug is 90% fixed.
27
28	### Tighten the loop
29
30	Treat the loop as a product. Once you have _a_ loop, tighten it:
31
32	- Can I make it faster? (Cache setup, skip unrelated init, narrow the test scope.)
33	- Can I make the signal sharper? (Assert on the specific symptom, not "didn't crash".)
34	- Can I make it more deterministic? (Pin time, seed RNG, isolate filesystem, freeze network.)
35
36	A 30-second flaky loop is barely better than no loop; a 2-second deterministic one is tight — a debugging superpower.
37
38	### Non-deterministic bugs
39
40	The goal is not a clean repro but a higher reproduction rate. Loop the trigger 100×, parallelise, add stress, narrow timing windows, inject sleeps. A 50%-flake bug is debuggable; 1% is not — keep raising the rate until it's debuggable.
41
42	### When you genuinely cannot build a loop
43
44	Stop and say so explicitly. List what you tried. Ask the user for: (a) access to whatever environment reproduces it, (b) a captured artifact (HAR file, log dump, core dump, screen recording with timestamps), or (c) permission to add temporary production instrumentation. Do not proceed to hypothesise without a loop.
45
46	### Completion criterion — a tight loop that goes red
47
48	Phase 1 is done when the loop is tight and red-capable: you can name one command — a script path, a test invocation, a curl — that you have already run at least once (paste the invocation and its output), and that is:
49
50	- [ ] Red-capable — it drives the actual bug code path and asserts the user's exact symptom, so it can go red on this bug and green once fixed. Not "runs without erroring" — it must be able to _catch this specific bug_.
51	- [ ] Deterministic — same verdict every run (flaky bugs: a pinned, high reproduction rate, per above).
52	- [ ] Fast — seconds, not minutes.
53	- [ ] Agent-runnable — you can run it unattended; a human in the loop only via `scripts/hitl-loop.template.sh`.
54
55	If you catch yourself reading code to build a theory before this command exists, stop — jumping straight to a hypothesis is the exact failure this skill prevents. No red-capable command, no Phase 2.
56
57	## Phase 2 — Reproduce + minimise
58
59	Run the loop. Watch it go red — the bug appears.
60
61	Confirm:
62
63	- [ ] The loop produces the failure mode the user described — not a different failure that happens to be nearby. Wrong bug = wrong fix.
64	- [ ] The failure is reproducible across multiple runs (or, for non-deterministic bugs, reproducible at a high enough rate to debug against).
65	- [ ] You have captured the exact symptom (error message, wrong output, slow timing) so later phases can verify the fix actually addresses it.
66
67	### Minimise
68
69	Once it's red, shrink the repro to the smallest scenario that still goes red. Cut inputs, callers, config, data, and steps one at a time, re-run

People who liked this also viewed

6 picks

Type