Stop Copilot changing your Excel file: use Chat only first, then let it edit

What are the three modes in Copilot in Excel?

I should give a little background first. Copilot in Excel used to be mostly a chat box that explained formulas and suggested charts. Then it learned to do the work itself, which is a feature Microsoft first called Agent Mode. It can now reshape data, merge sheets and build a whole report inside your workbook, and Microsoft treats that as a normal part of the Copilot pane and splits the behaviour into three modes.

Microsoft’s help page, Agent Mode in Excel, describes them clearly. Allow editing is for complex, multi-step tasks, and it changes the file. Plan creates a structured approach to the task, so you review that plan and confirm it before Copilot acts, and Chat only can analyse your workbook data and give you insights without making any changes to the workbook.

The phone column in the documentation matters more than it looks. Microsoft lists Android as chat mode only, and iPhone as chat mode with edit mode still rolling out. So if Copilot on your phone will not change a cell, that is caused by the platform and not your licence.

Why does Copilot change my workbook when I only asked a question?

The default setting causes most of the confusion, and Microsoft’s Copilot in Excel FAQ says it plainly. In editing mode, Copilot edits your workbook directly based on your requests, but you use chat mode to keep its responses contained within your chat. Edit mode is what you get when you open the pane unless you actively change it.

I see people mix questions and small requests in one sentence all the time when they type into that box. “Why is March low” is a question, and “Tidy up the region names” is an instruction. In edit mode Copilot answers the first part and does the second part. It does this on the real file instead of a preview.

You can see the difference on the same workbook. In Chat only, “which rows make March lower than February?” gets you a list of rows and a reason in the pane, and the sheet stays exactly as it was. In Allow editing, “fix the March numbers” can rewrite values, and Copilot decides what fixed means, so that second sentence is one I never type on a file I do not own.

How do I switch Copilot in Excel to Chat only?

You can open the Copilot pane and look at the controls around the box where you type. Microsoft’s pages show a mode menu there with the three choices, but some builds show an Allow editing control that you turn off and replace with Chat only. The labels have moved a few times this year, so if your screen does not match a screenshot you saw online, just look for the word Chat in that menu.

1. 01
   Open Copilot before you type anything

   Select the Copilot button to open the pane. Do not type the question yet.
2. 02
   Find the mode control

   It sits with the controls around the prompt box. If it says Allow editing, that is edit mode.
3. 03
   Choose Chat only

   Now your question can be answered, but nothing in the workbook will be changed.
4. 04
   Check it again next time

   Microsoft does not say that the mode stays chosen after you close Excel, so look at it each time you open the file.

I use that last step out of caution, and here is why I take it. Microsoft’s page about the model picker says the model you choose lasts only for the active session, and it goes back to the default when Excel closes. I wrote about that in why Claude is missing from the Copilot model picker, and while Microsoft’s pages do not say the same thing about the mode, they also do not say it sticks. So I treat it the same way and look before the first prompt.

What is the safe way to let Copilot edit a client file?

Chat only is not the whole answer because sometimes you do want Copilot to do the work. The value is in the order of the steps. You ask first, you read, and only then do you give it permission to change one thing, and then you check what it did using Excel’s own record instead of taking Copilot’s word for it.

1. 01
   Make sure there is a way back

   Work on a copy, or make sure the file is saved on OneDrive or SharePoint so Version History is there for you.
2. 02
   Ask in Chat only

   For example: "Which rows make March lower than February? Show me the row numbers." Read the answer and check two of those rows yourself.
3. 03
   Switch to Allow editing for one change

   Name the range and the result: "In the Region column of the Sales table only, trim the spaces and make the names consistent." One job per prompt.
4. 04
   Ask what changed

   Microsoft gives this exact prompt on its change history page: "What changes has Copilot made to this workbook?"
5. 05
   Check the totals yourself

   Work out one total by hand before and after, and compare. If they differ and you did not expect them to, stop there.

Step 4 uses a newer Copilot skill. Microsoft’s page, Review the change history of your workbook with Copilot in Excel, says Copilot can describe the changes made by a particular person or by Copilot itself, and Excel keeps supported changes for up to 365 days. But Copilot reads the same record that Show Changes keeps, so it has the exact same blind spots, and I went through every gap in what Copilot change history in Excel can and cannot see.

Step 5 is the step people skip, but it is the one that catches the real mistakes because a total that looks right can still be wrong. The method I use to check that is in how to check if ChatGPT or Copilot got your Excel numbers right. It takes about five minutes, and it does not depend on which AI did the work.

What do I do if Copilot already changed something I did not want?

I suggest you start with the quickest way back and move down only if you need to. If Copilot is still working, Microsoft says you can stop or pause it with the Stop button in the lower right corner of the chat input. That halts the job, but it does not put back what was already done.

Microsoft’s FAQ says that if you need to revert your changes, you can undo changes or view prior versions. Undo is fine for one small change you notice straight away. But for a multi-step job that touched three sheets, I would not try to count my way back with Ctrl+Z. I would open Version History instead because it gives you back the whole file exactly as it was, with every sheet and every format.

I have one warning about Show Changes. It records cell values and formulas, but it does not record formatting, charts, PivotTables, filters or hidden rows. So if Copilot recoloured a report or rebuilt a PivotTable, the pane can look clean even though the file has changed. That situation is exactly when Version History is the only honest answer.

When is Plan mode better than Chat only?

Plan sits between the two modes. You still get a real job done, but Copilot shows you the steps before it touches anything, and you confirm the plan first. It is the right mode for something like “merge these three monthly sheets into one table and add a summary”, because you want the work done but you want to make sure it plans to merge the right sheets before it starts.

You just have to remember that once you confirm, Plan behaves like an edit. The plan is a preview of the intent, and it is a plan of action rather than a picture of the final result. So the exact same after-checks apply, meaning you ask what changed and check one total yourself.

My own rule is very simple. I use Chat only for anything I am not sure about, Plan for a job with more than two steps, and Allow editing for one small change I can describe in a sentence. If you also use ChatGPT inside Excel on client files, I covered the privacy side of that in is ChatGPT for Excel safe for client files, and privacy is a different question from editing.