Get up to speed on an inherited workbook before you let AI change it
Work on a copy, inspect connections and named ranges, trace backwards from the outputs you need, and only then ask Copilot to describe what a sheet does.
Tools used
- Excel (Microsoft 365)Formula auditing tools and Inspect Workbook
- Copilot in ExcelDescribes what a sheet is trying to do
Step navigator
A copy of the workbook with your own notes on how the sheets connect, checked against the actual formulas.
Anyone handed a big workbook with no documentation.
Before you start
When someone on r/excel asked how to learn a large workbook they had been handed, the answers were consistent: copy it, ask the author if you can, inspect what is connected, and trace backwards from the outputs. A later thread adds that Copilot can describe what a sheet is trying to do. This guide puts those in order.
Step-by-step instructions
Make a copy and ask the author for a walkthrough
Work on a copy: "I'd first make a copy and work on that one in case you mess something up." If the person who built it is reachable, ask for a walkthrough; the top reply says to phone the creator, or whoever sent it or uses it most.
Inspect what is connected
Use the Inspect Workbook features for an overall picture, then "Look for evidence of VBA, data connections / Power Query, and named ranges."
Why this works
Hidden queries and macros change numbers without any formula showing it.
Find every formula cell at once
Go to Home → Find & Select → Go to Special → Formulas to highlight every formula cell. Ctrl+` switches to formula view, though one user warns it can make Excel "grumpy".
Trace backwards from the outputs you need
"Start at the end result(s) of the doc, particularly the parts that you need directly for your job functions, and walk backwards through the formulas and datasets." Use Formulas → Trace Precedents (click again to go more levels) and Ctrl+[ to jump to the cells a formula reads.
Ask Copilot what a sheet is doing, then check its answer
Once you know where to look, ask Copilot to describe a sheet's purpose. A user in the large-workbook thread: "Copilot can also be used if you ask it to describe what a spreadsheet is trying to do." Check each claim against the formulas you traced.
Describe what the Summary sheet calculates and which sheets feed it.
Why this works
An AI description is a starting point; the traced formulas are the evidence.
Write your own notes as you go
"If there is no documentation then start creating it yourself. This will help you in truly understanding how and why the spreadsheet works."
End of guide · Reviewed Oct 26, 2026
Pro tips2
- Colour the cells that hold typed values, not formulas, so you can see inputs at a glance; one r/excel user suggests exactly that.
- FORMULATEXT shows a formula next to its result.
Common mistakes3
- Changing anything in the original file.
- Starting at the first tab instead of at the output you need.
- Trusting an AI summary without tracing the formulas.
FAQ2
What if it has circular references?
Can AI read the whole thing for me?
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