The underline stays on the Mac
Local writing checks in Word, TextEdit, and Notes, with an optional rewrite that leaves the machine, and the token count left as the post's number.
- Category
- Productivity
- Who it is for
- A person who writes in Word, TextEdit, or Notes on macOS 14 and does not want every sentence in a cloud editor.
- Possible model
- Open source
- Difficulty
- Medium
- Inspired by
- DeAI · DeAI
- Original launch
- Watch the launch · Oct 9, 2026
Difficulty is an editorial estimate of technical and operational complexity, not a score.
Startup idea analysis by Startup Ideas. Last reviewed Oct 9, 2026. How we read a launch.
The startup idea
Adam posted DeAI on October 9. Inline writing hints tuned to your vocabulary. Custom rules. Optional AI rewrites in Word, TextEdit, and Apple Notes. macOS 14 or later. Open source. First launch needs manual approval. The post says nearly 300 million tokens in 4 days, mostly cached. The readme says real-time suggestions, a personal lexicon, and on-demand rewrites. Underlines for stock phrases, grammar via Harper, and leftover Markdown. You compare a rewrite before it applies. MIT. No telemetry and no DeAI account. Typing and local checks stay on the Mac. A cloud endpoint receives rewrite content under that provider's policy. For a local rewrite, use a server that actually runs on the Mac. API keys go in the Keychain. First launch needs Accessibility, and Gatekeeper may ask for Open Anyway. This page did not install the preview.
The opportunity is the underline that does not upload the draft. A smaller product is one app, local rules, a lexicon, and a rewrite that is optional and shown as a diff. The 300 million tokens are the post's number. The readme does not print them. The post says custom rules. The readme says a lexicon of replacements, words to avoid, and terms to preserve, and that rules can be turned off.
Do not treat the token count as a spec. Do not say a rewrite is local unless the model is the one on the Mac.
The problem
The stock phrase is in the sentence. The rewrite tool wants the whole document in someone else's cloud.
Who would pay for this?
- Primary
- A person who writes in Word, TextEdit, or Notes on macOS 14 and does not want every sentence in a cloud editor.
- Secondary
- Someone who will still send one paragraph to a model, after reading the diff.
- Early adopter
- One document, local underlines, the rewrite left off.
How could it make money?
Possible models. Nothing here is a claim about what DeAI charges.
- MIT. No price on the readme.
- A cloud rewrite is the provider's bill, not a DeAI plan. The repo does not print one.
What would the MVP look like?
- One Mac app, macOS 14 or later.
- Underlines from local rules.
- A lexicon the person edits.
- A rewrite you compare before it applies.
- The first-launch Accessibility step, written down.
How to validate the idea
- Ask five people to leave it on for a day in the app they already write in.
- If they only turn on the rewrite, the local check was not the product.
- Do not add a fourth app until one underline is accepted by someone who was not the author.
How to differentiate
- The draft stays on the Mac until a rewrite is asked for.
- The rewrite is a diff, not a silent replace.
- No DeAI account.
- Do not become another cloud document.
Why this could be interesting now
The post and the readme agree on the three apps, macOS 14, and the manual first launch. The token count is only in the post. The opening is one underline that never left the machine.
Original product launch
This launch is inspiration and evidence that someone shipped, not a partnership. The idea above is our reading of the broader opportunity. DeAI did not write it.
- Product
- DeAI
- Source
- DeAI
- Film
- DeAI, writing hints that stay on the Mac
- Posted
- Oct 9, 2026 · 0:29
Product that inspired this idea
Adam's post says he built DeAI: inline writing hints tuned to your vocabulary, custom rules, and optional AI rewrites in Word, TextEdit, and Apple Notes. macOS 14 or later, open source, and the first launch needs manual approval. The post also says nearly 300 million tokens in 4 days, mostly cached. The readme says MIT, no telemetry, no DeAI account, and that typing and local checks stay on the Mac. A cloud rewrite sends that text to the provider. API keys go in the Keychain. The first launch needs Accessibility, and Gatekeeper may need Open Anyway. The readme does not print the token count, or a price.
Posted by @leoooeth. Watch the original launch. No separate product site is listed unless the post itself is the source.
- writing
- macos
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