Comparisons
AI writing apps for Mac that work in every app
Every app in this category does roughly the same thing: you press a shortcut, your text is rewritten, and it goes back where it was. The model is not the differentiator any more. What actually decides whether you keep using one is how it is invoked, whether you can save your own instructions, and how it charges you.
The short version
If you want free and you have an Apple silicon Mac, start with Apple Intelligence Writing Tools — it is already installed and it costs nothing. Move to a paid app only when you hit its ceiling, which for most people is the fixed action list: you cannot add "reply to this in our support voice" as a button.
If you are technical and want to pay once, Kerlig ($49 one-time as of 2026-08-16) is the cheapest long-run option, because you supply your own API key and pay the model provider directly. If you want unlimited usage with nothing to configure, FixKey ($48/year as of 2026-08-16) is cheaper than we are and includes dictation.
KeigoButton is the one to look at if you also write on your phone, or if you write any Japanese. The buttons you build sync to an iOS keyboard, and the Japanese rewriting is the product's original purpose rather than a translation feature.
How they compare
| App | How you invoke it | Your own prompts? | Price | Notes |
|---|---|---|---|---|
| Apple Intelligence Writing Tools | Right-click or the Writing Tools menu | No — fixed action list | Free, built into macOS | Apple silicon only. No custom instructions. |
| Grammarly | Floating button in the text field | Limited (prompts in the AI panel) | Free tier; paid plans above it | Correction-first. The largest and most established. |
| Kerlig | Option+Space anywhere | Yes — custom actions | $49 one-time (1 Mac), $79 (2 Macs) | You bring your own API key, so tokens are billed by the model provider on top. 350+ models. macOS 12+. |
| FixKey | Custom shortcut anywhere | Yes — custom AI prompts | $48/year | Unlimited rewrites and unlimited speech-to-text, 180+ languages. |
| RewriteBar / Elephas / TextWisely | Menu bar or shortcut | Yes | Varies (TextWisely $29 one-time or $5/month) | Same category, different emphases — Elephas adds a knowledge base. |
| KeigoButton | Hover the bar at the bottom of the screen | Yes — buttons you write | Free for 50 rewrites/month; $12/month or $120/year for 1,000 | The same buttons appear on an iPhone keyboard. macOS 14+, Apple silicon and Intel. No API key needed. |
What actually separates them
1. Whether you can save your own instructions
This is the biggest practical divide. Apple Intelligence gives you a fixed menu — Friendly, Professional, Concise, Summarise. That covers the common cases and nothing else. Kerlig, FixKey and KeigoButton all let you write the instruction once and keep it as a button, which is what turns the tool from a novelty into something you press thirty times a day.
The test to apply: think of the edit you personally make most often. "Rewrite this so it does not sound passive-aggressive." "Turn these notes into a status update." "Reply declining, but leave the door open." If your tool cannot hold that as one press, you will keep going back to a chat window.
2. Whether it reaches the text or replaces your clipboard
Apps in this category read and write through the macOS Accessibility API, which is why every one of them asks for that permission on first run. The ones that do it properly replace the text in place. The ones that do not fall back to copying, which means your clipboard is clobbered and you lose whatever was in it.
Browsers and Electron apps (Slack, Notion, VS Code) expose their text fields differently from native ones, so this is where products diverge in quality. Test your actual daily apps during the trial, not TextEdit.
3. How it charges
- Bring your own key (Kerlig): cheapest at volume, but you manage an API key and a second bill. Good if you already have one.
- Flat subscription with usage included (FixKey, KeigoButton): nothing to configure, predictable, more expensive per rewrite at high volume.
- Free (Apple Intelligence): no cost, no custom prompts, Apple silicon only.
Which to pick
- You just want typos and tone fixed, for free → Apple Intelligence Writing Tools, already on your Mac.
- You want the most established product and correction is the main job → Grammarly.
- You are technical, high-volume, and want to pay once → Kerlig.
- You want unlimited usage plus dictation, cheaply → FixKey.
- You write on your phone as much as your Mac, or you write Japanese → KeigoButton.
Try this kind of rewriting free, in the browserFour modes, two candidates each. No install, no account, five a day.
Where KeigoButton fits
KeigoButton started as a Japanese keyboard, and that is still where it is strongest: 敬語 (keigo) is the honorific register Japanese business writing requires, and getting it right is a forced edit on nearly every message. The Mac app applies the same idea to English — your own saved instructions, run against the text under your cursor, in any app. The thing none of the Mac-only tools above do is follow you onto a phone keyboard with the same buttons.
Frequently asked questions
Is there a free AI writing app for Mac?
Yes — Apple Intelligence Writing Tools is built into macOS on Apple silicon Macs and costs nothing. Grammarly and KeigoButton both have free tiers as well (KeigoButton's is 50 rewrites a month). The limitation of the free built-in option is that you cannot add your own instructions; you get Apple's fixed list of actions.
Which AI writing app for Mac works in every application?
Kerlig, FixKey, Elephas, RewriteBar, TextWisely and KeigoButton all work system-wide by using the macOS Accessibility permission to read and replace text in whatever app you are in. Grammarly works in most apps through its own floating interface. Quality varies most in browsers and Electron apps like Slack and Notion, so test the apps you actually use.
Why do these apps need Accessibility permission?
Reading the text in another application's text field, and writing the replacement back into it, is only possible through the macOS Accessibility API. It is the same permission text-expansion and dictation utilities require. It does not grant screen recording or keystroke logging, and it can be revoked in System Settings at any time.
Is Kerlig or FixKey cheaper than KeigoButton?
Both, on price alone, as of 2026-08-16. Kerlig is $49 once for one Mac, though you supply an API key and pay the model provider separately. FixKey is $48 a year with unlimited rewrites. KeigoButton is $120 a year for 1,000 rewrites a month, and is worth the difference only if you want the synced iPhone keyboard or you write Japanese.
Try it on your Mac
Free for 50 rewrites a month, no card required. macOS 14 or later, Apple silicon and Intel.