Why this skill exists
Every organization runs on a handful of workbooks nobody fully understands anymore. The person who built the model left; the “temporary” override from 2024 is still there; the SUM range stops at row 500 and the data now reaches 612. These files mostly still produce numbers — which is exactly the problem, because a workbook that errors gets fixed and a workbook that’s quietly wrong gets presented.
This matters double in the Copilot era. “Analyze this spreadsheet” works beautifully on clean tabular data and fails silently on merged headers, numbers-stored-as-text, and three tables sharing a sheet. Before you trust any AI analysis of a legacy workbook, someone has to establish what the workbook actually is. That someone can now be Cowork — under strict rules.
The rule that defines this skill: audit only. It never modifies the file, never refreshes a connection, never “helpfully fixes” a formula. An auditor that edits the books isn’t an auditor.
What it does, step by step
- Inventories every sheet — including hidden ones — with purpose, data extent, and cross-sheet references. A sheet it can’t explain gets “Purpose unclear”, not a plausible-sounding story.
- Maps the cell population — inputs vs formulas vs the silent killers: hardcoded overrides, where someone typed a number over a formula and the cell stopped updating. Every override gets a cell address.
- Flags fragility — merged cells, mixed types in columns, hardcoded range limits that exclude new rows, embedded totals, multiple tables per sheet, color used as data, external links (listed, never refreshed).
- Proposes a cleanup list — numbered, prioritized by impact-to-risk, each item stating what it unlocks (“unmerge headers → sheet becomes table-convertible”). Proposes. Nothing executes.
- Saves the audit report as a Word doc in your OneDrive Cowork output folder and gives you a 10-line summary leading with the worst finding.
Install (60 seconds)
- Download the SKILL.md above.
- In OneDrive, create the folder
/Documents/Cowork/skills/workbook-auditor/. - Drop SKILL.md inside — “Workbook Auditor” shows up as a chip in Cowork’s side panel.
- Say: “Audit [workbook name]” and point it at the file.
Make it yours (5 minutes, recommended)
- The fragility checklist — Step 3 lists our universal offenders. Add your org’s: volatile functions in big models, VBA you’ve banned, specific naming conventions.
- The report destination — point the audit doc at the SharePoint library where your team keeps model documentation, so audits accumulate next to the files they describe.
- The priority logic — we order cleanup by impact-to-risk. If your goal is specifically Copilot-readability, reorder to put table-structure fixes (unmerge, one table per sheet, headers in row 1) first.
Failure modes we’ve already handled
| What goes wrong | How the skill handles it |
|---|---|
| It “helpfully” fixes the workbook while auditing | Hard rule: zero modifications, ever — cleanup happens later, on a copy, item by item |
| Refreshing external links pulls stale or unauthorized data | Connections are listed, never refreshed |
| It invents purposes for mystery sheets | ”Purpose unclear” is the required honest answer; open questions go to the owner |
| Findings are vague (“some data issues”) | Every claim must carry a cell or range address — vagueness is banned by the style rules |
| Hidden sheets get skipped | Inventory explicitly includes hidden sheets, marked as such |
The bigger idea
The audit report is documentation the workbook never had — and it outlives the audit. Hand it to the file’s owner and you’ve converted tribal knowledge into a document. Run the cleanup and you’ve converted a haunted file into something both humans and Copilot can analyze without superstition. Either way, the spreadsheet stops being a single point of failure with a person’s name on it.