AI Writing Assistant for Windows, in Every App

Translate Text Without Switching Tabs

Select text in any app and translate it into 35+ languages. The result appears where you are working, with no browser and no separate translator. Great for non-native speakers, remote teams, and multilingual workflows.

Change Tone in One Click

Rewrite any text to match the tone you need. Polish a work email, make a social post pop, or soften a blunt message, all in one click.

Fix Grammar & Spelling in Any App

Catch spelling and grammar mistakes and awkward phrasing before they reach Send. WindowSill checks your text in context, so corrections actually fit what you meant.

Save Custom AI Prompts

Build custom AI prompts for social posts, report summaries, code formatting, or any writing task you repeat. Save an instruction once and run it from any app.

Your Text, Your Model, Your Choice

WindowSill doesn't force you onto one AI vendor. Connect your own API key from providers like OpenAI or Anthropic, or keep everything private by running a local model through Ollama, so your writing never leaves your machine. It's the flexibility power users on Windows have been missing.