Nebula Writer vs. Microsoft 365 Copilot

If you want an AI agent to edit your Word, Excel and PowerPoint files, Microsoft's answer is Copilot, and on personal plans it comes with a Microsoft 365 subscription. Nebula Writer is a desktop app that opens .docx, .xlsx and .pptx files and has an AI agent that edits them, with no Microsoft 365 plan needed. The editor is free forever with a monthly AI allowance; Pro is $15 a month for more AI.

Copilot is the better choice for many people. This post covers what each costs, where each one fits, and the limits on both sides.

What each costs

Prices below are for individual plans in the US, as of October 2026, from Microsoft's plan comparison page.

Microsoft 365 Basic has no AI features, and business plans are priced differently. If you only need to edit Office files and don't need AI, Microsoft says Word, Excel and PowerPoint for the web are free to edit with a Microsoft account. That may be all you need.

Where Copilot is the better choice

• You already pay for Microsoft 365. Copilot works inside Microsoft's own apps, so it fits best when your work already lives there.
• Exact Office rendering matters. Word, Excel and PowerPoint are the reference for their own formats. Nebula Writer has its own editors, so a complex Word layout can look slightly different there.
• Several people edit the same file at once. Microsoft's apps support co-authoring. Nebula Writer does not offer live co-editing.

Where Nebula Writer fits

• You don't have, or don't want, a Microsoft 365 subscription. Open the .docx, .xlsx or .pptx file in Nebula Writer and ask the agent to change it.
• You want the file itself edited. The agent changes the document through the format's own structure. In Word that means paragraphs, tables, comments, tracked changes, headers and footers. In Excel it means cells, formulas, number formats and charts. In PowerPoint it means shapes, slides, speaker notes and native charts. It reuses the styles already in the file. More on this in what the agent can do in each format.
• Your project mixes formats. A report, its workbook, a deck and your Markdown notes can sit in one folder, and you can point the agent at any of them with @. It handles LaTeX too; see Nebula Writer vs. Overleaf.
• You want to approve each change. Every change waits for your decision. Discard puts the file back exactly as it was.

Nebula Writer runs on macOS (Apple silicon), Windows and Linux. You sign in with a Google account.

A real example: a rate shown as a fraction

On October 3, 2026 we gave the agent a small sample workbook we built for testing. Cell B4 ("Conversion rate") held the formula =B2/C2 and displayed 0.125. This was the prompt:

Review layout-review.xlsx and make the conversion rate display as a
percentage with one decimal place. Keep the formulas, stored values, other
formatting, and workbook layout unchanged. Check the saved appearance before
telling me it is ready. Leave the Archive sheet and archive copy alone.

Afterwards B4 displayed 12.5%. The formula was still =B2/C2, the stored value was still 0.125, and the Archive sheet was untouched. Only the cell's number format changed.

In the app, a change like this appears as Review workbook edit, with Keep edit and Discard edit. See the AI spreadsheet editor for more workbook examples, and the AI presentation editor for decks.

Limits to know

• Office edits are one decision. You can inspect each change the agent made to a Word, Excel or PowerPoint file, but you keep or discard them together. Change-by-change decisions are for Markdown, LaTeX and plain text.
• Check complex Word files in Word. Before you send a contract or a file with macros, fields or many tracked changes, open it in Microsoft Word. The Word editing guide lists what Nebula Writer supports.
• Slide renders need LibreOffice. The agent can look at rendered slides only when LibreOffice is installed on your computer.
• Web and academic search are Pro features.
• AI runs in the cloud. Your request and the parts of your documents the agent needs are sent to our servers and our AI provider. Your files stay in your folder.

Which to choose

Choose Copilot if you already have Microsoft 365, your team co-authors files, or your work already lives in Microsoft's apps.

Choose Nebula Writer if you want an AI agent for Word, Excel and PowerPoint files without a Microsoft 365 plan, if your projects mix Office files with LaTeX or Markdown, or if you want to keep or discard every change.

The editor is free. Download Nebula Writer or compare plans. To see how review works, read how to check every AI edit or the guide to reviewing changes and undoing them.