Cotabby brings AI autocomplete to almost every text field on your Mac. It is a free, open-source macOS app — maintained by two students and released under the AGPL-3.0 license — that runs its models locally on your device. The project has gathered over 1,000 stars on GitHub and is under active development, with updates landing in October 2026.
As you type in Mail, Notes, a browser, or just about any other app, Cotabby shows a gray ghost-text suggestion inline next to your cursor. Press Tab to accept it a word at a time, or simply keep typing to ignore it. The default engines — Apple Intelligence and open-source on-device models powered by llama.cpp — run entirely on your Mac, so no account, cloud round-trip, or telemetry is involved. If you prefer a bigger model, an optional OpenAI-compatible engine can point at a server you configure yourself. The result feels like the inline completion you know from code editors, except it follows you across your whole system, from email drafts to chat windows.
Beyond plain completion, Cotabby adds small workflow touches that fit how people actually write: inline macros expand shortcuts into quick calculations, unit and currency conversions, dates, and random values, while emoji autocomplete lets you type a shortcode and accept the character without leaving the field. Prediction behavior is configurable in detail — you can choose whether it predicts ahead, suggests completions inside words, and shows following words — so the assistant can be tuned from conservative to aggressive to match your writing style and the app you are typing in.
Cotabby is free and open source, with no account or subscription required. The maintainers accept voluntary support, but every feature ships in the free build.
Cotabby is for Mac users who write all day — emails, documents, messages, code comments — and want Copilot-style completions everywhere they type, without sending their keystrokes to the cloud.