Fix Grammar in Slack on Mac — 4 Best Methods

Why Grammar in Slack Actually Matters

Slack has quietly become the place where professional reputations are built and damaged. You might spend an hour crafting a polished email to a client, but then fire off dozens of Slack messages throughout the day without a second thought. The problem is that those Slack messages are read by your manager, your teammates, your skip-level — and they form impressions based on what they see.

A message that reads "Their going to need the report by wendsday, can you make sure its ready?" sends a signal, whether you intend it to or not. In channels with dozens of people, a sloppy message lives forever in searchable history. When you're communicating cross-functionally or with leadership, grammar errors erode credibility in a way that's hard to measure but impossible to ignore.

The irony is that Slack — the tool where professional communication happens most frequently — has no grammar checker. The desktop app on Mac relies on macOS system spell check, which catches "teh" but has nothing to say about subject-verb agreement, awkward phrasing, or tone. If you want real grammar correction in Slack on Mac, you need to bring your own solution.

Here are four methods, ranked from simplest to most effective.

Method 1: macOS Built-in Spell Check

How to enable it: Go to System Settings → Keyboard → Input Sources → Edit, then make sure "Correct spelling automatically" and "Show inline predictive text" are turned on. Alternatively, in Slack itself, right-click any text field and verify that Spelling and Grammar → Check Spelling While Typing is enabled.

Once enabled, macOS will underline misspelled words with a red dotted line. Right-click the word to see suggestions, or press Cmd+; to jump to the next misspelling.

What it does well: It catches obvious typos like "recieve" or "definately." It's free, built into the operating system, requires no installation, and works in every Mac app including the Slack desktop client. For basic spell check, it's perfectly adequate.

What it doesn't do: It doesn't catch grammar errors. "Me and him went to the meeting" won't get flagged. Neither will "Your welcome," "could of," or "I would be appreciate if you could send." It doesn't understand sentence structure, verb tense consistency, or whether your message reads clearly. It also autocorrects words sometimes in ways you don't want, turning proper nouns and technical terms into nonsense. For anything beyond basic spelling, macOS spell check falls short.

Method 2: Use Slack in a Browser with Grammarly

How to set it up: Open Slack in Chrome or Edge at app.slack.com. Install the Grammarly browser extension. Grammarly will now check grammar in Slack's web interface, showing underlines and suggestion popups as you type.

What it does well: Grammarly provides real-time, inline grammar suggestions. It catches grammar errors, not just spelling mistakes. It understands tone, clarity, and even suggests rewording for conciseness. If you're writing a long, important message, the real-time feedback is genuinely helpful. The free tier handles the basics; the Premium tier ($30/month) adds advanced suggestions.

The trade-offs: You have to abandon Slack's desktop app. The browser version of Slack is functional, but you lose native macOS notifications (browser notifications are less reliable), performance takes a hit with many workspaces open, and you're adding yet another always-open tab to your browser. If you're the kind of person with 30+ tabs open already, running Slack as one more tab creates friction. You also can't use this method in any other desktop app — Teams, Notion, VS Code, and everything else still have no grammar checking. For a deeper comparison of Grammarly vs Brow, see our detailed breakdown.

Method 3: Copy-Paste to ChatGPT or Another Grammar Tool

How it works: Select your text in Slack, copy it (Cmd+C), switch to ChatGPT (or any grammar tool — LanguageTool, QuillBot, etc.), paste the text, ask "fix the grammar," wait for the result, copy the corrected text, switch back to Slack, select the original text, and paste the corrected version.

What it does well: The grammar correction quality from ChatGPT is excellent. It handles complex sentence restructuring, tone adjustment, and can even follow custom instructions like "make this more professional" or "simplify this." If you need a complete rewrite rather than a quick fix, ChatGPT is genuinely powerful.

Why it's slow: The workflow takes 30–60 seconds per correction. That doesn't sound like much, but multiply it across a dozen messages a day and you've lost 10+ minutes just on context switching. More importantly, the copy-paste dance breaks your mental flow. You were composing a thought in Slack, and now you're navigating to another app, waiting for a response, copying text, switching back. By the time you return to Slack, you've lost the thread of the conversation you were in.

For a single important message, this method works. For everyday Slack communication, the friction is too high for most people to sustain. That's why most people simply stop doing it after a few days.

Method 4: Brow — Select, Shift+Shift, Done

How to set it up: Download Brow (free during beta), open it, and grant accessibility permissions when prompted. That's the entire setup.

How it works:

1. Select text in Slack's desktop app (or any Mac app)
2. Press Shift twice (double-tap Shift)
3. Text is corrected in place in about one second

The corrected text replaces your selection right where you typed it. No copying. No pasting. No switching apps. No browser required. You stay in Slack the entire time.

Brow works by using macOS accessibility APIs to read and replace selected text system-wide. It sends your selected text to an AI model, receives the corrected version, and inserts it back into the text field — all within the desktop app you're already using. This means it works in the Slack desktop app, not just the browser version.

Beyond Slack, the same shortcut works in Microsoft Teams, Notion, VS Code, Terminal, Apple Notes, Apple Mail, Pages, Xcode, Discord, Telegram — every Mac app that supports text selection. You learn one shortcut and it works everywhere.

Brow is built in native Swift, not Electron, so the entire app uses about 50 MB of RAM. The grammar fix is just one of 15+ tools included — you also get a launcher, clipboard manager, window manager, screenshot tool, and more. See what Mac apps Brow can replace for the full picture.

Comparison: All 4 Methods Side by Side

Feature	macOS Spell Check	Browser + Grammarly	ChatGPT Copy-Paste	Brow
Correction speed	Instant	Real-time	30–60 seconds	~1 second
Friction	Low	Medium	High	Low
Catches grammar errors	No	Yes	Yes	Yes
Works in Slack desktop app	Spell only	No (browser only)	Via copy-paste	Yes
Works in other Mac apps	Spell only	No	Via copy-paste	Yes
Cost	Free	Free / $30/mo Premium	Free / $20/mo Plus	Free (beta)
Requires app switching	No	Yes (to browser)	Yes	No

Which Method Should You Use?

If you just need spell check and don't care about grammar, enable macOS built-in spell check and move on. It's free, zero-friction, and handles basic typos without any installation.

If you're already using Slack in a browser and have Grammarly installed, you're in a decent spot. Grammarly's inline suggestions are excellent for catching grammar errors as you type. The downsides — browser-only, extra RAM usage, subscription cost for Premium — might not matter to you.

If you need a single important message rewritten, pasting into ChatGPT makes sense. The quality of the rewrite can be outstanding, especially if you give specific instructions. But it's not a sustainable daily workflow.

If you want grammar correction in the Slack desktop app (and every other Mac app) without changing your workflow, Brow is the most practical option. One shortcut, works everywhere, no subscription, no browser required. It won't give you Grammarly's real-time inline suggestions or ChatGPT's deep rewriting capabilities, but for the common case — quickly fixing a message before you hit Send — it's the fastest path from typo to polished text.