The board deck is due tomorrow morning, and the numbers on the summary tab don't tie out. Somewhere across forty tabs of a model someone else built, a cell that used to feed the total got overwritten, deleted, or quietly changed to a hard-coded number three revisions ago. You're the one who has to find it — not because you built the model, but because you're the one still awake.
Why tracing a formula was always the slow part
Spreadsheets don't explain themselves. Excel's own "trace precedents" tool shows you one arrow at a time, and a real model runs that chain through six or seven tabs before it reaches a number you can check by hand. If you didn't build the workbook, you're re-learning someone else's logic under a deadline. And every AI assistant you'd normally reach for — a chat window, a copilot bolted onto a document — could only see whatever text you pasted in. None of them could see the live formula, the named range, or the tab three sheets over that the formula was quietly pointing at.
What actually changed
Claude for Excel is a sidebar add-in — an extra panel built into Excel itself, not a separate app you switch to — that reads your open workbook directly: every tab, every named range, every formula, all at once. Anthropic ran it as a research preview for Enterprise customers from October 2025, then opened it to every Pro subscriber in January 2026. It now sits on the Pro, Max, Team and Enterprise plans, inside Excel on the web, Excel on Windows with a current Microsoft 365 subscription, and Excel on Mac version 16.46 or later.
- Works: Excel on the web, Excel on Windows (Microsoft 365), Excel on Mac 16.46+.
- Doesn't work: Excel 2016 or Excel 2019 as a perpetual or volume-license copy — there's no subscription connection for the add-in to use.
Trace the error inside the actual workbook
Instead of clicking through precedents tab by tab, you ask it directly, and it answers with a citation — a clickable reference to the exact cell it's talking about, the same way a footnote points to a source. Anthropic's own documentation shows the kind of chain it will walk: a Q3 revenue figure traced back through an assumptions tab, a pricing tab, a forecast tab, and finally the summary cell that pulled from all three. It can trace `#REF!`, `#VALUE!`, `#DIV/0!` and circular-reference errors the same way, ending in a plain-English sentence about which upstream cell caused the break and why.
Summary!C22 should equal Forecast!B14 but it's off by about 8%.
Trace the formula chain between them and tell me exactly which
upstream cell has changed, and what it changed from.Then build the report, not just fix it
The same access to live formulas works in the other direction. Describe the report you need in plain English, and it builds the structure with the formulas already linked — not a static table of numbers you'd have to wire up yourself. Change an assumption afterwards and the downstream cells recompute correctly, because it's editing real formulas, not overwriting them with values.
Build a monthly budget-vs-actual variance report from the Budget
and Actuals tabs. One row per line item, a variance column in both
currency and percentage, and flag anything over 10% variance in a
separate summary section. Link every cell to the source tabs.Turn it into a skill so nobody re-explains it next month
In March 2026, Anthropic added Skills to the Excel and PowerPoint sidebars — the same idea we covered in Claude Skills, applied inside a spreadsheet instead of a coding agent. Once someone on your team has the variance-report prompt above working exactly right, they save it as a one-click action in the sidebar, and it's available to everyone else on the plan — nobody re-types it, and nobody's version drifts from anyone else's.
What it replaces, and what it doesn't
It replaces the hours someone spends as the team's de facto formula-tracer, the Slack thread trying to work out who broke the model, and the ritual of rebuilding the same report structure from scratch every month. It doesn't replace deciding which assumptions are the right ones, or what a number actually means for the business — that judgement stays yours. And it doesn't turn Excel into a database: a workbook with hundreds of thousands of rows, or one that five people need to query at once, belongs in an actual database, no matter how well an assistant reads around Excel's limits.
Check before you paste in real numbers
Anthropic's default is to use Free, Pro and Max conversations to train future models unless you switch off "Help Improve Claude" in privacy settings; Enterprise accounts are exempt by default. If your company is on Team, don't assume either way — check the admin console before you open payroll, a client's model, or anything else you wouldn't want retained.
Where it's the wrong tool
Skip it for a five-line spreadsheet — fixing it yourself is faster than describing it. Skip it, too, the moment the real problem is that the workbook has outgrown Excel; moving the data is the fix, not a better way to read around the limit. And whatever it hands back, check it the way you'd check a junior analyst's first draft before it goes in front of a client or a board — it will rebuild a wrong assumption just as confidently as a right one.
The useful version of this is that the spreadsheet finally explains itself. The part that doesn't change is that someone still has to be the one who checks.
The skill that used to matter in a finance or ops role was knowing where the numbers were hiding. That's worth less every month a tool like this improves. What's worth more is knowing which number to ask about in the first place, and catching it when the answer is wrong — and that's a judgement no add-in makes for you.
If you're not sure which of your team's recurring reports are worth wiring up this way, and which ones still need a real engineer, that's exactly the kind of call we help make in an AI Opportunity Assessment.