Sill streams any Mac window to iPhone or iPad with touch, Pencil and keyboard input

An open window, beamed to your pocket

An open-source project called Sill lets you view and fully control any window from your Mac — or its entire desktop — on an iPhone or iPad, relaying touch, trackpad, keyboard and Apple Pencil input back to the computer. The project's repository, which surfaced on the front page of Hacker News, describes a system with no accounts and no intermediary server: the video and the input travel directly between the two devices over an encrypted connection.

How it works

According to the repository's documentation, Sill for Mac lives in the menu bar and captures the selected window with ScreenCaptureKit, then encodes it as HEVC video using VideoToolbox, preferably on the Mac's hardware encoder. The stream travels over a TLS 1.3 connection straight to the Sill app on the iPhone or iPad. Nothing is captured while no device is connected.

When the encoder or the link falls behind, Sill drops frames rather than queuing them, so the picture stays current — a deliberate trade of smoothness for responsiveness.

Input returns along the same connection: taps, clicks, momentum scrolling, keystrokes and Pencil strokes, which the Mac app converts into mouse and keyboard events via the macOS Accessibility permission. A keyboard attached to the device types on the Mac as soon as the picture appears, and three-finger swipes and pinches invoke Mission Control, App Exposé and Spaces much as they would on a Mac trackpad. The app's own menus are reachable from the device too, appearing in the iPad's native menu bar on iPadOS 26 or later.

Connections and pairing

Devices can connect in several ways: over the same local network using Bonjour discovery, over a USB cable, over peer-to-peer Wi-Fi via a Direct Wireless Connection mode that works the way AirDrop does, or remotely through the user's own VPN, such as Tailscale, with a Remote Access option enabled.

Each iPhone or iPad is paired with the Mac once, using a 12-digit code that can be scanned with the camera or typed by hand; afterwards every connection is pinned to the exchanged keys. The documentation warns that Sill for Mac 0.3.1 and earlier left local-network connections unencrypted and accepted connections without pairing, so anyone running an old build should update.

Notable features

• The clipboard works in both directions, but only for text, up to 256 KB at a time. Sill never reads the device clipboard unprompted, and passwords marked as concealed by a password manager stay on the Mac.
• An Aa control resizes the streamed window on the Mac so its text appears at the size you pick on the device, then restores the window's original size and position when streaming stops.
• An optional virtual display mode moves the streamed window onto a display of its own so it keeps updating when other windows cover it. It relies on a private macOS API, which the developer cites as one reason the Mac app ships from its website rather than the Mac App Store.
• On the iPhone Duo, the app follows the hinge: flat open fills the inner display, half open puts the picture above a trackpad and keys, and closed shifts to the cover display.

Availability and limitations

Sill for Mac is a free, notarized download from getsill.app, also installable through Homebrew, and requires an Apple silicon Mac on macOS 14 or later. The iPhone and iPad app is free on the App Store and can be built from source; devices need iOS 17 or iPadOS 17 or later. Funding comes from optional tips via GitHub Sponsors, which unlock nothing — every feature is free.

The limitations are worth knowing: one window or the desktop at a time, no audio from the Mac, a text-only clipboard, and the Mac must be awake with Sill running, which the app may not be able to arrange itself.

Why it matters

Apple's own tools stop short of this. Sidecar turns an iPad into a second display and Universal Control shares input, but neither streams a single existing Mac window to a phone with full remote control over it. Sill effectively turns an iPhone or iPad into a wireless terminal for any Mac application — including professional software that will never get an iOS version. The architecture matters as much as the feature: direct TLS-encrypted connections with no server in between, hardware HEVC encoding and aggressive frame dropping make it fast and private by design, and the open-source license lets others inspect or extend it. The one private API, kept out of the Mac App Store as a result, is a small illustration of where Apple's sandbox limits tools that try to do genuinely new cross-device tricks.