Installation¶

Seamless CAD installs like any other Blender add-on, from a .zip. There is nothing else to install — the geometry kernel and every library it needs are inside that zip.

If you just want to start modelling, do the four steps below and go to the Quick Start. The rest of this page is for when something does not go the way it should.

Requirements¶


Blender	4.2 or newer. Tested on 4.2, 4.3, 4.4 and 5.1
Windows	10 or 11, 64-bit. This is the released product
macOS	Apple Silicon, macOS 11+. Included in the release, but unverified in use — see Testing builds
Linux	x86-64, glibc 2.34+. Included in the release, but unverified in use — see Testing builds
Disk	About 135 MB once installed

No separate CAD software, no CAD licence, and no runtime to install alongside. The Microsoft Visual C++ runtime is bundled too, so you do not need to install that either.

Install¶

In Blender, open Edit > Preferences > Add-ons
From the ∨ menu at the top right of that panel, choose Install from Disk…
Select the CAD_<version>_install.zip file you were given
Enable the add-on in the list

Then press N in the 3D viewport to open the sidebar. A Seamless tab appears there. That tab is the whole interface.

This ships as a classic add-on, not as a Blender Extension. The zip contains no blender_manifest.toml, so drag-and-drop onto the Blender window and the Extensions repository listing do not apply to it. Use Install from Disk….

Where it lands¶

Knowing this is useful when updating or when reporting a problem. The installed folder is named CAD_8_1_5_1 regardless of the version in the filename — the directory name has not been renamed as versions advanced.


Windows	`%APPDATA%\Blender Foundation\Blender\<version>\scripts\addons\CAD_8_1_5_1`
macOS	`~/Library/Application Support/Blender/<version>/scripts/addons/CAD_8_1_5_1`
Linux	`~/.config/blender/<version>/scripts/addons/CAD_8_1_5_1`

Two consequences:

Updating overwrites in place. Installing a newer zip replaces the same folder, so you do not accumulate old copies — but you also cannot have two versions installed side by side in one Blender.
The folder name is not the version. Read the version from Edit > Preferences > Add-ons, or from the zip filename you installed. Do not read it from the folder.

First start¶

Open the Seamless tab and press Start Seamless CAD.

This launches the geometry kernel — a separate executable that does the actual CAD computation — and creates your first part. The first start takes a moment because a process is starting up. Later sessions reuse it.

Blender and the kernel talk over a local TCP socket on 127.0.0.1, port 8080. Nothing leaves your machine. If your firewall asks, you can safely deny it access to public networks; only the loopback connection matters.

Port 8080 is fixed and there is no setting for it. If another program is already listening on 8080 — a web dev server is the usual culprit — the add-on assumes it is a leftover kernel from a previous session and tries to use it. CAD operations then fail with no obvious cause. It logs one line about this, so if nothing computes, check whether 8080 is taken, free it, and re-enable the add-on.

The kernel is told Blender's process ID and shuts itself down if Blender disappears, so a crash does not normally leave the port occupied.

Updating¶

Install the new zip the same way as above
Restart Blender

Restarting matters more than it does for pure-Python add-ons: the old kernel process and the loaded native libraries are not swapped out by re-enabling the add-on alone.

Files you have already saved keep working — the Feature Tree is stored in the .blend file, not in the add-on.

Uninstalling¶

In Edit > Preferences > Add-ons, expand Seamless CAD and use Remove.

A .blend file saved with CAD parts still opens afterwards; the proxies and collections remain as ordinary Blender objects, but nothing recomputes and the Seamless tab is gone. Anything you want to keep independently of the add-on should be baked or exported first.

If the tab does not appear¶

No Seamless tab in the sidebar. The add-on is installed but not enabled, or Blender is older than 4.2. Check the checkbox in Edit > Preferences > Add-ons.

The tab is there but empty below the workspace panel. That is normal before a part exists. Press Start Seamless CAD, or pick a part from the Active CAD Workspace dropdown.

The tab is there and nothing ever computes. The kernel is not running. Edit > Preferences > Add-ons, expand Seamless CAD, and look at CAD Engine: Running / Not running — that reads the real process state. See Troubleshooting.