Install Fillet

Install on the Mac

You need a Mac with Apple silicon (M1 or newer) and macOS 15 or later. Intel Macs aren’t supported.

Download the newest Fillet-<version>.dmg from Fillet’s releases on GitHub.
Open the disk image and drag Fillet into Applications.

Open Terminal and run:

xattr -dr com.apple.quarantine /Applications/Fillet.app

Open Fillet from Applications.

You only do this once. Updates that Fillet installs itself arrive without the quarantine flag, so they open straight away.

Why the Terminal step?

Fillet isn’t signed with an Apple Developer ID or notarized by Apple. macOS puts a quarantine flag on everything you download, and it won’t open a quarantined app that Apple hasn’t checked: it says it can’t verify that Fillet is free of malware.

The xattr command removes that flag. -d deletes it and -r does so for every file inside the app, including the fillet-mcp helper that Claude Desktop starts. The app itself doesn’t change.

Keep it up to date

While Check for updates automatically is on, Fillet looks for a new release once a day. When there is one, an orange Update button appears in the window’s toolbar. Click it, then Install Update. The new version replaces the old one when Fillet quits, or straight away with Relaunch Now.

To look yourself, choose Fillet › Check for Updates…

Install on iPad

Fillet isn’t on the App Store or TestFlight. To use it on iPad, build it from source in Xcode on a Mac and run it on your iPad, which needs iPadOS 18 or later.

Install Xcode, CMake and XcodeGen, and follow Build in the README. Building the geometry kernel takes about 30 minutes, once.
Put your Apple team ID in App/Local.xcconfig: DEVELOPMENT_TEAM = ABCDE12345.
Open App/Fillet.xcodeproj, pick the Fillet scheme and your iPad, and click Run.

With a free Apple Account, an app you install from Xcode stops opening after seven days. Run it from Xcode again to renew it.

Questions and answers

macOS still says Fillet can't be opened.: Run the command on the copy in Applications, not the one in the disk image, and type the path exactly. Or open Fillet once, then go to System Settings › Privacy & Security, scroll down and click Open Anyway next to the message about Fillet.
Claude Desktop says fillet-mcp can't be opened.: The helper inside the app is still quarantined. Run the xattr command above, then restart Claude Desktop.
Does Fillet run on an Intel Mac?: No. Fillet is built for Apple silicon only.
Do I need an account?: No. Fillet never asks you to sign in.