WindowSill - Free AI Command Bar for Windows

TL;DR

TL;DR: WindowSill is a free Windows command bar that brings AI writing assistance — grammar check, tone rewriting, and translation — directly into any app via a global hotkey. It also ships clipboard history, media controls, and reminders out of the box.

What Is WindowSill?

WindowSill is a Windows-native productivity bar that lives in the system tray and springs to life via a global hotkey. Unlike browser extensions that only work inside web apps, WindowSill intercepts selected text system-wide and runs it through AI-powered tools regardless of which application you’re in.

The core pitch: you select text anywhere, press Alt+Space, and get instant access to grammar correction, tone adjustment, text rewriting, and translation across 35+ languages — without switching windows or copy-pasting into a separate tool.

It sits in the background consuming minimal RAM and stays out of your way until you need it.

Features

From the official product page:

• AI writing assistant — grammar and spell check on selected text
• Text rewriter — adjust tone (formal, casual, professional, etc.)
• AI translation — 35+ languages, works in any app
• Custom AI prompts — define your own rewriting/transformation rules
• Clipboard history — searchable history of recent copies
• Media controls — system-wide playback control (Spotify, YouTube, etc.)
• Short-term reminders — set quick in-app reminders
• Unit converter — built-in quick conversions
• Web browser control — play/pause/forward/rewind any web media
• App launcher — launch apps and URLs from the command bar
• Customizable extensions — community-made extensions available

The free tier includes all core productivity features. WindowSill+ ($4/month) unlocks AI writing assistance (grammar, rewriting, tone, translation). WindowSill Pro adds organization-wide management, graduated pricing for teams, and BYOK (bring your own key) for OpenAI, Anthropic, Google, and local LLMs.

Setup

Install

Download from the Microsoft Store:

# Search "WindowSill" in the Microsoft Store app
# Or visit directly:
https://apps.microsoft.com/detail/9PG6CJPXTPZ0

No install wizard — it lands in your Start menu and system tray automatically.

First Launch

1. Open WindowSill from the Start menu
2. It will request Accessibility permission (required to read selected text globally)
3. The icon appears in the system tray
4. Press Alt+Space to open the command bar

Enable AI Features

1. Click the system tray icon → Dashboard
2. Under WindowSill+, click Start Free Trial (7-day trial)
3. Or go to Settings → AI and add your own API key (Pro only)

How It Works

WindowSill registers a global hotkey (Alt+Space by default) that opens a floating overlay. The overlay reads the currently selected text via Windows Accessibility APIs, sends it to the AI backend (or your own API key), and returns the result to a side panel — all without switching focus from your active app.

User selects text in any app
        ↓
Alt+Space opens WindowSill overlay
        ↓
Selected text sent to AI (or your own API)
        ↓
Result shown in side panel → click to copy/replace

This design means it works inside VS Code, Slack, Notion, Gmail, or any other Windows application — no per-app extension needed.

Practical Evaluation Checklist

• ✅ Works in any Windows app via Accessibility API
• ✅ Grammar and spell check with one keystroke
• ✅ Tone rewriting (formal, casual, professional, friendly)
• ✅ 35+ language translation
• ✅ Clipboard history with search
• ✅ Media controls for web and desktop players
• ✅ Custom AI prompts (define your own rewrite rules)
• ✅ Free tier covers all non-AI features
• ⚠️ AI features require WindowSill+ ($4/month) or Pro
• ⚠️ Requires Windows 10/11 with Accessibility permission

Security Notes

WindowSill needs Accessibility permission to read selected text. This is a broad permission — review the privacy policy before enabling on a work machine. The Pro tier’s BYOK option lets you route AI requests through your own API keys, avoiding WindowSill’s servers entirely for AI processing.

FAQ

Q: Is WindowSill free? A: Yes, the core productivity features (clipboard history, media controls, reminders, unit converter, app launcher) are free forever. AI writing assistance requires WindowSill+ ($4/month) after a 7-day free trial.

Q: Does it work with my own API key? A: WindowSill Pro supports BYOK for OpenAI, Anthropic, Google, and local LLMs. This keeps AI text off WindowSill’s servers.

Q: How is it different from PowerToys Run? A: PowerToys Run is a file/app launcher with plugin support. WindowSill is focused on text manipulation — selecting text and running AI operations on it. They coexist fine.

Q: Does it work on Linux or macOS? A: No — WindowSill is Windows-only, using Windows Accessibility APIs.

Source and Accuracy Notes

• Project page: getwindowsill.app
• Microsoft Store listing: apps.microsoft.com/detail/9PG6CJPXTPZ0
• GitHub organization: github.com/WindowSill-app (no public repo as of publish)
• HN launch thread: news.ycombinator.com/item?id=45346593
• License: Proprietary (not open source)
• Source last checked: 2026-06-19