Sanity Check

Sanity check

"This goes to the CFO in an hour. Is there anything embarrassing in it?"

Not are these the right numbers — no file can answer that. Is this artifact internally consistent, and will it survive a reader looking for holes? This is the five minutes a careful colleague spends cross-footing the totals, checking the date, and noticing that slide 1 and slide 9 disagree.

The product is the severity ranking. A flat list of eleven nitpicks is worth the same as no list, because the reader has an hour and will read three lines. Deciding what blocks sending is the skill.

This is a one-artifact skill. Given two periods and asked what changed, that is whats-changed's job, not this one — see Boundary below.

Workflow

1. Take the artifact

One file: .xlsx, .xlsm, .csv, .tsv, .pptx, .pdf, .docx, or pasted text. Read it with references/extraction.md, which also tells you what each format hides — you cannot find a hardcoded cell in a PDF, and you must say so rather than implying the file is clean.

Ask nothing unless genuinely blocked. At most two questions, and only these:

• Several candidate data tabs and no obvious primary → "Which tab is the one going out?"
• A convention can't be inferred and changes the verdict, e.g. whether a column is deliberately signed negative → ask.

Never ask what to check. The check list is this skill's, not the user's.

2. Walk the twelve checks

Read references/checks.md and walk its twelve families in order. Anything not in those twelve is not a finding, however interesting.

3. Tier every finding

Three tiers, each with a mechanical test, first match wins:

• Blocker — a number on the page is wrong, or cannot be verified. Someone may act on a false figure.
• Embarrassment — the numbers are defensible, but a reader will ask a question you can't answer.
• Hygiene — safe to send as is, worth fixing before it rots.

The reference carries the per-check tier assignments, including the one case that is genuinely computable rather than judged: a typed-over cell is a Blocker when it disagrees with what its formula would produce and Hygiene when it agrees.

4. Write the verdict, then the findings

**Two blockers — don't send yet.** Plus one date that will draw a question.

## Blockers (2)
- B1 `Summary!C12` totals £4,182k; the detail tab's rows sum to £4,201k. £19k apart, and the
  summary figure is the one on slide 1.
- B2 `Detail!F31` is `#DIV/0!` and feeds the margin column, so every margin below row 31 prints
  blank.

## Embarrassments (1)
- E1 The Headcount tab is dated "as at 30 Sep" in a November pack.

## Hygiene (1)
- H1 `Detail!D14` is typed in where the rest of column D is a formula. It agrees with the
  formula today, so nothing is wrong yet.

Checked: totals and cross-footing · share columns · impossible percentages · duplicates ·
error cells · formula overrides · signs · as-of dates · placeholders · units · cross-tab
agreement · displayed rounding.

Ask "why is B1 a blocker?" or "show me B1" to see the cells and the arithmetic behind any finding.

The verdict line comes first and says whether it is safe to send. "Safe to send, two things worth fixing" is the sentence the user came for. Omit a tier's section entirely when it is empty; keep the count in every heading that appears. Every finding opens with its handle — B, E, H plus its number within the tier.

The scope line is mandatory and always identical — the same twelve family names, in the canonical order above, every run, whatever the artifact. A clean bill of health is worthless if the reader can't tell "nothing found" from "nothing looked for", and a scope line that varies with the file is a scope line that drifts.

The caveat clause after the list has one admission rule, and it is narrow. Add a clause only when a family was impossible to check in this artifact — the format hides what it needs:

• ✅ "formula overrides and error cells aren't visible in a PDF" — the format makes it impossible. Without this, the reader thinks those checks passed.
• ✅ "the deck gives no as-of date anywhere" — the input the check needs is absent.
• ❌ "no share columns exist, so that check had nothing to fire on" — it was checked and found nothing. That is the clean result the list already reports.
• ❌ "single tab, so no cross-tab comparison" — same: checked, nothing to find.
• ❌ "every value is typed, so no formula column to stand out against" — same.

Checked and clean needs no clause. Could not check does. If nothing was impossible, the scope line ends at displayed rounding. The fixed trace line follows it, and nothing else does.

Rules

• Never judge the numbers against the world. "Revenue looks low for Q3" is a claim the file cannot support. Internal consistency is the whole remit.
• Report, don't repair. Don't rewrite the artifact, and don't offer to — an offer invites a second turn that rewrites someone's workbook. Fix it only if asked outright.
• Precision over recall. One invented finding costs more than one missed nitpick, because the reader then has to check your checking. When something is genuinely borderline, say so in one clause rather than promoting it a tier.
• Nothing outside the twelve families. Formatting taste, business advice, escalation suggestions, and limitations of your own analysis are not findings. "No unit counts, so margin can't be checked" belongs in the scope line's caveat, never in a tier.
• A stated convention disarms its check. If the sheet says "rounded to nearest £k", components not summing exactly is expected and is not a finding. But a convention excuses only what it covers — a rounding note does not excuse a gap three orders of magnitude larger than the rounding step, and using it that way is the one way to get the arithmetic wrong while sounding careful.
• Cite a locator for every finding. Summary!C12, slide 4, table row 3, p.7 Table 2. A finding without a cell reference can't be acted on in the hour available.
• When the artifact is clean, say so plainly and stop. Verdict line, the scope line, the trace line. No padding, no reassurance paragraph, no "you may wish to consider".
• Two files given? Still sanity findings, tiered, for both. The comparative sharpens the stale-figure checks and nothing else. Do not produce a variance report — if what they wanted was what moved, say so in one line and point at whats-changed.

Tracing

The findings are one line each, so the reader's next move is to open the cell and push back. Read references/tracing.md before answering any follow-up: it carries the handles (B, E, H, scope), the fixed closing line (and its clean-verdict variant), the trace block (Cells · Arithmetic · Tier · What would change it), and the questions to expect — "why is that a blocker? it's tiny", "it adds up when I check it", "which number is right?", "the sheet says rounded — isn't that why?", "what did you actually check?".

A trace re-opens the file and corrects the list if a finding doesn't reproduce. Pushback alone never moves a tier.

Boundary with whats-changed

Four checks overlap — reconciliation, stale dates, mixed units, hardcoded cells. That is expected: the same defect matters to both, but one mentions it in passing and this one exists to find it. "Check this month's numbers" is ambiguous between them: if the request is about movement, it is the other skill.