--- name: Anomaly Investigation slug: anomaly-investigation category: Data description: Anomaly Investigation diagnoses a known data anomaly by forming candidate causes, testing them against the data, and eliminating those the evidence refutes. Use it when you already have a spike, drop, or outlier and need the confirmed root cause and supporting evidence. github: "https://github.com/gaasher/Agent-Loop-Skills/tree/main/loops/anomaly-investigation" language: Python stars: 166 forks: 19 install: "npx degit https://github.com/gaasher/Agent-Loop-Skills/tree/main/loops/anomaly-investigation ~/.claude/skills/anomaly-investigation" installs_to: ~/.claude/skills/anomaly-investigation source_path: loops/anomaly-investigation/SKILL.md collection_size: 25 category_size: 812 collection_url: "https://dirskills.com/collections/gaasher/Agent-Loop-Skills" added: 2026-09-08T05:34:40.083Z last_synced: 2026-09-08T05:34:40.083Z canonical_url: "https://dirskills.com/skills/anomaly-investigation" --- # Anomaly Investigation Anomaly Investigation diagnoses a known data anomaly by forming candidate causes, testing them against the data, and eliminating those the evidence refutes. Use it when you already have a spike, drop, or outlier and need the confirmed root cause and supporting evidence. **Install:** ```bash npx degit https://github.com/gaasher/Agent-Loop-Skills/tree/main/loops/anomaly-investigation ~/.claude/skills/anomaly-investigation ``` ## README # Anomaly Investigation Loop A **form → test → eliminate → confirm** loop — root-cause analysis as a search. The artifact is an investigation log; the feedback signal is the count of **live candidate explanations**, driven down toward a single cause that is **confirmed**, not merely consistent. Each iteration you test one candidate against the data and drop the ones the data refutes, narrowing the field until one survives. The discipline this enforces: a cause is "root" only when it both **survives an honest attempt to refute it** and makes a **positive prediction that checks out** (e.g. "if this is the cause, removing it restores normal" — and it does). A story that merely *could* explain the anomaly is a hypothesis, not a finding. ## When to use Use this when an anomaly is already in hand — you know roughly what looks wrong and want the cause diagnosed by elimination against the data. Default to a broad initial slate of mutually distinguishable causes, then test the one that splits the field fastest; if the anomaly is vague, your first job is to make it precise (iteration 0). Not for open-ended exploration of a dataset with no anomaly to chase (use data-analysis), and not for verifying an external claim against the literature (use claim-verify). ## Setup Resolve bindings interactively. If `loop.run.yaml` exists in the working dir, load it, confirm the values in one line, and skip to the loop. Otherwise: on Claude Code (the `AskUserQuestion` tool is available) infer a likely value for each binding and present it as the recommended option; on other hosts ask each as a quoted plain-text prompt. Then write `loop.run.yaml` (format: `examples/run.example.yaml`) and confirm the values before creating any other files. | binding | meaning | default | how to infer | |---|---|---|---| | `` | data (or logs) to investigate; read-only ground truth | — | scan the working dir for a data/log file | | `` | what looks wrong: the metric, where/when, and how big the deviation is | — | ask the user; make precise in iter 0 | | `` | interpreter that runs analysis snippets in the user's env | `python3` | `pyproject.toml`/`.venv`/`uv` in the working dir | | `` | output investigation log | `/investigation.md` | — | | `` | where snippets + ledger live | `./sandbox` | — | | `` | max iterations | 8 | — | Analysis snippets run in the **user's environment** via ``, so they may use whatever the user has installed. Keep helper code **stdlib-first** (`csv`, `statistics`): if a snippet needs `pandas`/`numpy`, probe with `try/except ImportError` and degrade to a stdlib path, or offer a consented `uv pip install "pandas=="` — never assume the package is installed. ## The loop Copy this checklist and tick items off: - [ ] Iteration 0 — characterize the anomaly precisely; form an initial slate of candidate causes in ``. - [ ] Pick a candidate to test (the one whose test most cleanly splits the remaining field). - [ ] Test it: write `/iter/test.py`, run with ``, redirect to `out.txt`. - [ ] Eliminate (data refutes it → drop from the live set) or advance (data supports it → keep it live). - [ ] Confirm the survivor: when one candidate leads, run a positive test only it predicts, after a refutation attempt. - [ ] Append a ledger row; stop when one cause is confirmed or at ``. **Iteration 0 — characterize.** Quantify the anomaly precisely: write and run a snippet that pins down *what* deviated, *where/when*, and *how big* the deviation is against the normal baseline (the same metric on surrounding periods/segments). Then **form an initial slate of candidate causes** — mutually distinguishable explanations, broad enough to contain the truth (a real change, a composition/mix shift, a data-quality bug, a measurement change, seasonality, an outlier segment). List them in `` as the live candidates. Record nothing as confirmed yet. **Then, until stop (one confirmed cause, or budget):** 1. **Pick a candidate to test.** Ideally the one whose test most cleanly splits the remaining field, so each iteration removes as many live candidates as possible. 2. **Test it.** Write `/iter/test.py` that computes the thing that would **refute or support** it (slice by segment/source/time, recompute the metric, compare distributions). Run it with ``, redirecting output to `/iter/out.txt` (never flood your context). 3. **Eliminate or advance.** - Data **refutes** it → mark it eliminated in `` with the evidence; drop it from the live set. - Data **supports** it → keep it live, and if it is now the leading candidate run a **confirming test**: a positive prediction it uniquely makes (e.g. "remove / seasonally-adjust the suspected factor → the anomaly disappears"). Also try to **refute** it — a leading candidate that survives a genuine refutation attempt and passes its confirming test is the root cause. 4. **Log** one ledger row and continue, narrowing the live set. **Observational equivalence.** Two mechanistically different candidates can make *identical* predictions in the data you have (e.g. a bot flood and a pipeline double-count both look like "sessions spike, conversions flat" in daily aggregates). When that happens you cannot separate them here — do not pick one arbitrarily. Report them as a single confirmed cause **at the resolution of the available data**, and name the additional data that would distinguish them (finer-grained logs, raw event records, an upstream check). Distinguish, too, the **mechanism** (how the metric moved) from the **root cause** (why the inputs were wrong) — confirming the mechanism is progress, but is not the cause. ## Ledger `/ledger.tsv`, tab-separated, never commas in the text. Header: ``` iter candidate_tested verdict live_candidates ``` `verdict` ∈ {`characterize`, `refuted`, `supported`, `confirmed`}. Example: ``` iter candidate_tested verdict live_candidates 0 characterize anomaly + slate characterize 5 1 real drop across all segments refuted 4 2 one segment's conversions fell refuted 3 3 one source's sessions inflated supported 2 4 removing that source restores normal confirmed 1 ``` Report the confirmed root cause with its confirming evidence, the alternatives and how each was ruled out, and — if you stop without a single confirmed cause — the remaining live candidates and the test that would separate them. ## Constraints - **Confirm, don't just fit.** The root cause must survive an honest refutation attempt *and* pass a positive confirming test; "consistent with the data" is not enough, since several stories usually are. - **Test against the data, not intuition** — every elimination and the final confirmation is backed by a computation you ran, recorded in ``. - **Keep candidates distinguishable** and prefer the test that splits the field fastest, so the live count falls; do not chase one pet theory while leaving alternatives untested. - **Only read ``** — never modify it, because it is the ground truth every test is checked against. The sandbox is self-contained (no `../` escapes). - Do not pause the loop to ask whether to continue; run until a cause is confirmed or the budget is hit. ## Stops - **Confirmed** — exactly one candidate survived refutation and passed a positive confirming test. - **Budget** — `` iterations reached without a single confirmed cause; report the live set.