Design with AI agents
Allow agent connections, paste one command, then ask Claude for a part. You watch it build in your open design, one step at a time, and you can undo any step you don't want.
Turn on agent connections
Fillet speaks MCP, the protocol AI agents use to work in other apps. It stays off until you turn it on.
- Open the design you want the agent to work in.
- Tap Agents, the sparkle at the right end of the toolbar, and turn on Allow agent connections.
- Open the design you want the agent to work in.
- Choose Design › Allow Agent Connections, or click Agents, the sparkle in the toolbar, and select the Allow agent connections checkbox.
Connect Claude Code
The popover writes the one command Claude Code needs. You only do this once.
- Tap Copy command.
- On a Mac on the same Wi-Fi, paste it into Terminal and press Return. Universal Clipboard or AirDrop gets it there.
- Click Copy command, or choose Design › Copy Agent Setup Command.
- Paste it into Terminal and press Return.
On iPad the command ends in a token, Authorization: Bearer …, which tells your iPad the Mac is yours. Keep it to yourself. If the iPad gets a new address, copy the command again.
Use Claude Desktop or another MCP client
Claude Desktop starts its own tools, so it uses a small helper inside Fillet for the Mac. The helper finds the running app by itself.
- In the Agents popover on the Mac, click Copy Claude Desktop config.
- In Claude Desktop, choose Settings › Developer › Edit Config.
- Paste the entry into
claude_desktop_config.json, insidemcpServersif it’s already there, then quit and reopen Claude Desktop.
{
"mcpServers": {
"fillet": {
"command": "/Applications/Fillet.app/Contents/Helpers/fillet-mcp",
"args": ["--connect"]
}
}
}Other clients connect the same way: give them the address from the popover if they speak HTTP, or the helper if they only start commands.
Ask for a part
Ask Claude in plain words, with the design open in Fillet:
> In Fillet, make a wall bracket with two M4 screw holes.The agent names the design, then adds one step at a time. A pill over the view names the agent and the step it’s on.
With several designs open, the agent works in the one you used last.
Undo an agent’s step
Agent steps go into the same undo history as yours.
- Tap Undo at the top right, or press ⌘CmdZ, to take back the agent’s last step.
- Tap Redo, or press ⇧Shift⌘CmdZ, to put it back.
To change an agent’s step, tap it on the timeline. To remove it, touch and hold it (on the Mac, Control-click it), then choose Delete. The agent can undo its own steps, but never one of yours unless it names it.
Questions and answers
- What can an agent do?
- Almost everything you can: sketch, extrude, revolve, fillet, chamfer, shell, holes with the same screw presets, combine, move, mirror, pattern, parameters, colours, print check and export. It looks at a picture of its work, and can turn your view to show you. A step that fails, such as a fillet too big for its edge, never lands in your design: the agent gets the reason and tries again.
- What are Scale and Loft steps?
- Steps only an agent can make. Tap one on the timeline to change it in the inspector, like any other step.
- Can an agent build with Fillet closed?
On the Mac, yes. Add the helper inside the app with a file name:
claude mcp add fillet-headless -- \ /Applications/Fillet.app/Contents/Helpers/fillet-mcp \ ~/Designs/bracket.filletIt makes the file if needed and saves after every step. Open it in Fillet when the agent is done.
- Does my design leave my device?
- Not through Fillet. A Mac only accepts programs on that Mac, and an iPad only devices with the token. The agent itself may send what it reads to its own service.
- The popover says “Can't listen”.
- Another app holds the ports. Fillet tries 7878, then 7879 to 7888. Quit the other app, then turn Allow agent connections off and on again.
- The agent can't reach my iPad.
- Keep Fillet open on the iPad with the design showing, put the Mac on the same Wi-Fi, and copy the command again.