Charm and Kerlig are both Mac writing tools you buy once rather than rent, which is rare enough to be worth comparing properly. They do different jobs. Kerlig is an on-demand AI assistant: you select text, press Option and Space, and ask a model to rewrite, translate or summarise it. Charm is continuous mechanical correction: it fixes spelling and grammar and predicts your next word as you type, entirely on-device, and never touches your wording. Plenty of people would be well served owning both.
What does each app actually do?
Kerlig puts a model behind a keyboard shortcut. Press Option and Space in any Mac app and a panel appears over your selected text, ready to rewrite, shorten, translate, change tone, answer a question or draft a reply. Nothing happens until you invoke it, and you choose which model handles the request.
Charm works the other way round. It runs quietly in the background and corrects as you type. Spells fixes misspellings the moment you finish a word, Polish tidies grammar when you finish a sentence, and Oracle offers the next word for you to accept with Tab. There is no panel to summon and nothing to select. Correction happens inline, wherever the cursor already is.
That difference in timing shapes everything else. Kerlig is for the moments you stop and think about a piece of text. Charm is for the small mechanical slips you would rather never think about at all. Our roundup of Mac writing assistants covers where each type fits.
Is Kerlig really a one-time purchase?
Yes, with one caveat worth knowing before you buy. Kerlig sells perpetual licences rather than a subscription: a Basic tier at around $49 for one Mac, a Pro tier at around $79 for two Macs, and a higher team tier. Prices move, so check kerlig.com before deciding.
The caveat is that the licence covers the app, not the intelligence. Because Kerlig routes requests to AI providers using your own account, you also pay whoever runs the model for the tokens you spend. For light use that is small change. For heavy daily rewriting on a frontier model it adds up, and it is a variable cost rather than a fixed one. Running a local model through Ollama or LM Studio removes that bill entirely.
Charm has no second bill: $9.99 once, up to 3 Macs, a 14-day money-back guarantee, and no usage costs, because every correction runs on your own machine.
Do you need an API key to use Kerlig?
For most cloud models, yes. Kerlig supports a very wide catalogue, over 350 models across providers including OpenAI, Anthropic, Google, Mistral and others, and you connect them by pasting in your own API key. That is genuinely powerful if you already hold provider accounts, and you are never locked to one vendor.
It does mean setup: an account with a provider, a generated key, billing added, the key pasted into Kerlig, a default model picked. Local options such as Ollama, LM Studio and Apple Foundation Models skip the key, though the first two need their own install and model download.
Charm asks for none of this. You install it, grant Accessibility and Input Monitoring permission, and start typing. No account, no key, no model shopping. Our guide to setting up a writing assistant on Mac covers that first run.
| Feature | Charm | Kerlig |
|---|---|---|
| Price | $9.99 once, 3 Macs | Around $49 once, 1 Mac |
| Ongoing costs | None | Your own AI token bill |
| Setup needed | Permissions only | API key or local model |
| Corrects as you type | Yes | No, invoked on demand |
| Word prediction | Yes, Oracle | No |
| Rewrites your text | No, mechanics only | Yes, its core strength |
| Works in browsers | Via Fix Selection shortcut | Yes, same shortcut everywhere |
| On-device | Always | Only with a local model |
Which one works better in browsers and Electron apps?
Kerlig has the cleaner story here. Because it works on a selection you make yourself and pastes a result back, the Option and Space shortcut behaves the same in Chrome, Slack and native apps alike.
Charm's live correction is at its best in native Mac apps, where the Accessibility API gives it reliable read and write access to your text. Chromium-based apps do not support the same range-based text writes, so in browsers and Electron apps Charm switches to Fix Selection: highlight the text, press Option-Command-V, and Charm corrects it in place.
That still fixes the text, but it is a deliberate action rather than something that happens on its own. If most of your writing happens in a browser, weigh that honestly.
Where does Kerlig genuinely win?
Kerlig does far more than Charm. It rewrites, summarises, translates, shifts tone, drafts replies and chats with documents, all from one shortcut. Charm does none of that by design.
It also gives you the model catalogue. Access to hundreds of models, including frontier ones, means a rewrite is limited by your provider budget rather than by what fits on your Mac. If a new model launches next month, Kerlig can use it.
Its reception backs this up: Kerlig reached #3 product of the day on Product Hunt with several hundred upvotes, and it runs on macOS 12 or later, an older baseline than Charm's macOS 14. It is a well-made app with a real audience.
Where does Charm win?
Charm wins on cost, effort and restraint. It is $9.99 once with no token bills, no API keys and no model to choose. Install, grant two permissions, type. For anyone who wants correct writing rather than a writing assistant to manage, that gap in setup matters more than it sounds.
It also wins on the thing it refuses to do. Charm fixes mechanics and never rewords you, so what lands in the message is still your sentence, only spelled and punctuated correctly.
And it is on-device with no cloud path at all, which means it works offline, skips password fields, and sends nothing anywhere. We explain why that matters in our piece on on-device AI privacy.
Frequently asked questions
Is Kerlig a subscription or a one-time purchase?
Kerlig is a one-time purchase, with a Basic licence at around $49 for one Mac and a Pro licence at around $79 for two Macs, plus a higher team tier. There is no monthly app fee. The nuance is that you pay your own AI provider for the tokens you use on top of that, unless you run a local model. Charm is $9.99 once for up to 3 Macs with no usage costs at all.
Do I need my own API key to use Kerlig?
For most of the cloud models Kerlig supports, yes. You add your own key from a provider such as OpenAI, Anthropic or Google, and you are billed by that provider for usage. Kerlig also supports local options including Ollama, LM Studio and Apple Foundation Models, which avoid API keys and token bills. Charm needs no key and no account of any kind.
Does Charm rewrite or reword my writing?
No. Charm deliberately fixes mechanics only: spelling, grammar and the next word it predicts you are typing. It never rewords a sentence or changes your tone. If you want rewriting, tone changes, summarising or translation, that is exactly the job Kerlig is built for and Charm is not.
Can I use Charm and Kerlig at the same time?
Yes, and for a lot of people that is the sensible answer. They occupy different moments: Charm runs continuously in the background correcting mechanics as you type, while Kerlig sits behind a shortcut for when you want a model to rewrite, translate or summarise something. Together they cost less than a year of most writing subscriptions.
Does Kerlig work offline like Charm?
Only if you point it at a local model such as Ollama, LM Studio or Apple Foundation Models. With a cloud provider selected, Kerlig sends your selected text to that provider and needs a connection. Charm is on-device by default with no cloud mode at all, so it works on a plane and skips password fields.