Grammarly vs Microsoft Copilot: Style Rules or 365 Drafting

The short answer: if your company already runs Microsoft 365 and the bottleneck is producing first drafts from your own documents, mail and meetings, Microsoft's Copilot Business add-on does it inside Word, Outlook and Teams for $18 per user a month, paid yearly, shown down from $21 (Microsoft Copilot business pricing). If the bottleneck is ten writers drifting from the brand's names and tone, Grammarly Pro keeps them on one style guide and brand tone in every app for $144 per member a year (Grammarly pricing article). Both checked on 26 October 2026.

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Copilot writes with your company's context. Grammarly checks against your company's rules. A team can need one, both or neither, and the expensive mistake is buying the drafting tool to fix a consistency problem.

What decides it:

1. The bill for the team, worked out. For example, ten people on the Copilot Business add-on cost 10 x $18 x 12 = $2,160 a year on top of their Microsoft 365 licences; ten on Grammarly Pro cost 10 x $144 = $1,440 (Microsoft pricing, Grammarly pricing article).
2. What your writers already have open. If their day runs through Word, Outlook and Teams, Copilot meets them there. If it runs through a CMS, LinkedIn and Google Docs in a browser, Grammarly's extension is already where they type.
3. The count that proves it. Pick ten recent pieces and log every correction the reviewer made: facts and structure on one side, names, spelling and tone on the other. The bigger column tells you which tool to trial.

Where each one shows up

From Grammarly's support pages, the agent builder article, the Grammarly pricing article and Microsoft's Copilot business pricing, read on 26 October 2026.

A difference in kind

Drafting from your files, or checking against your rules

Microsoft sells Copilot as AI built for work: drafting and chat grounded in your work data, inside the Office apps, with agents for research and data analysis (business pricing). It is strong where the first draft depends on what is in your SharePoint and inbox. Grammarly's team features run the other way: a single style guide and a single brand tone on Pro, with no cap on Enterprise, applied while people write (plans page). It is strong where the draft exists and the question is whether it says "MarketingOS" or "Marketing OS" today.

The Office add-in is on its way out

Grammarly is retiring Grammarly for Microsoft Office: the add-in will get no more security or feature updates or support, and Grammarly recommends its Windows app, which works with Office 2016 and newer on Windows 10 and 11 (retirement notice). On a locked-down corporate laptop, a desktop app is a different IT request from an add-in. Ask before you buy seats.

Agents on both sides

Grammarly's agents now sit in Superhuman Go, from the company that owns Grammarly, and the Grammarly how-to builds one that checks drafts against a brief. Microsoft's Agent Builder makes declarative agents for Microsoft 365 with knowledge from SharePoint and Copilot connectors (Agent Builder). The step below uses Microsoft's, because its documentation names this exact job.

Building a writing coach in Agent Builder

Microsoft lists, as an Agent Builder example, an agent that provides writing coaching tailored to organisational standards (Agent Builder). Build it from microsoft365.com/chat or Teams: give it the brand book and the naming list stored in SharePoint as knowledge, and instructions to review a pasted draft against them and list each departure with the rule it breaks. Test it on three old posts before sharing it.

The human check is built into how it works: the writer pastes a draft, reads the list, and decides line by line. The agent comments; it does not edit the file or publish. Two limits from Microsoft's page to plan around: Agent Builder cannot call external services without moving the agent to Copilot Studio, and SharePoint sources have to be shared with the right people by hand.

Start free

Both have a no-cost tier to test against real work. Grammarly Free fixes mistakes, shows the tone of a draft and includes 100 AI prompts a month (plans page); Microsoft's business page offers Copilot Chat to try, and its personal plans compare their usage with a free tier (business pricing, individual plans). Run your correction log for two weeks on the free tools before paying for either.

Read Microsoft's plan cards to the footnote. They include Copilot in the apps, while Cowork, Autopilot and agent usage are billed as you use them (business pricing), so the seat price is where the bill starts, not where it ends. Ask what agent usage will cost a month before the agents reach the whole team.

The verdict for a Microsoft 365 team

• Choose Grammarly if your job is brand consistency across many writers and many apps, browser included, at a lower price per head.
• Choose Microsoft Copilot if your job is drafting, summarising and answering from the company's own files, mail and meetings, for a team that lives in Microsoft 365.

Sometimes the correction log shows something else: Grammarly on some laptops, Copilot on others, ChatGPT on personal cards, and nobody owning the style guide. Then the stack is the problem rather than any one tool, and a fixed one-week review like the Startup Fixer, which I sell, maps it before another subscription is added.

The Grammarly entry covers its plans; Grammarly belongs to Superhuman, covered in the Superhuman entry. Copilot has no entry here; its pricing lives on microsoft.com.

FAQ

Does Grammarly still work in Word?

Through Grammarly for Windows, yes, with Office 2016 and newer on Windows 10 and 11; the older Office add-in is being retired (retirement notice).

Is Copilot included in Microsoft 365 for one person?

Microsoft 365 Personal, $9.99 a month on monthly billing, includes the Word, Excel, PowerPoint and Outlook desktop apps with Microsoft Copilot, at higher usage than the free tier (individual plans, checked on 26 October 2026).

What does Microsoft 365 Business Standard with Copilot cost?

$23.50 per user a month paid yearly, which bundles the apps, business email and Copilot; Business Premium with Copilot is $32 (business pricing, checked on 26 October 2026).