bimai
Using bimai

Civil 3D bridge

Let your bimai team read the drawing open in Civil 3D (alignments, profiles, surfaces, corridors and pipe networks) through a local bridge on your own computer.

Not built yet

Design stage. This describes how the feature is intended to work and may still change. The bridge is built and tested against Autodesk's Civil 3D 2025 and 2027 APIs, but it hasn't been run inside a real Civil 3D yet. Please test it with the checklist below and report what you find.

Autodesk's own AutoCAD and Civil 3D MCP server only works inside Autodesk Assistant. So bimai brings its own: the Civil 3D bridge, a small add-in that Civil 3D loads at startup. It lets your bimai team read the drawing you have open, on your own computer, and nothing else.

bimai team (Claude Code) ──▶ http://127.0.0.1:27184/mcp ──▶ bridge inside Civil 3D ──▶ your open drawing

What it can do

Read-only, on the drawing that is active in Civil 3D:

ToolAnswers questions like
get_drawingWhich units and coordinate system does this drawing use? How many alignments and surfaces are there?
list_layers, count_objectsWhich layers are frozen? How many objects are on layer C-ROAD?
list_alignments, get_alignmentWhich alignments are there, how long, and which profiles do they have?
alignment_point, alignment_stationWhere is station 1+250 at 3.5 m offset? At what station is this point?
profile_elevationsWhat are the design levels every 20 m along A2-MAIN?
list_surfaces, surface_elevationsWhat are the lowest and highest levels of the existing ground? What is the level at these points?
list_corridorsWhich corridors are out of date, and which assemblies do they use where?
list_pipe_networks, get_pipe_networkWhich pipes have less than 0.8 m cover? Which pipes run between which structures?

All values are in drawing units. Pipe slopes are absolute values. Invert levels are not calculated: Autodesk's API doesn't say whether a pipe's start point is its centre or its invert, so the bridge reports what is defined (points, diameter, slope, cover) instead of guessing.

Safe by design

  • It never changes your drawing. Everything is opened read-only.
  • It never interrupts your work. While you are in a command, the bridge answers "Civil 3D is busy" and waits for you; it doesn't take over the drawing.
  • It is only reachable from your own computer. It listens on 127.0.0.1 only and refuses requests from web pages or other machines.
  • Nothing is sent anywhere by the bridge. It answers your bimai team on the same computer.

Install

Needs Civil 3D 2025, 2026 or 2027 on Windows. In your project folder:

bimai connect civil3d

That's it. bimai asks "Install it now?", downloads the bridge, checks that it is exactly the version bimai expects, installs it, and connects your team to it. If you picked Civil 3D during bimai init, bimai offers this straight away.

Why Windows asks for permission

During the install, Windows asks: "Do you want to allow this app to make changes to your device?" That is expected:

  • The bridge is installed in C:\Program Files\Autodesk\ApplicationPlugins. That is the one folder Civil 3D always trusts, so the bridge loads without security warnings, also on company PCs where Civil 3D only loads add-ins from trusted folders (SECURELOAD set to 2).
  • Only administrators may write to Program Files, so Windows asks you once.
  • bimai copies the verified bridge there and changes nothing else. Click Yes.

No administrator rights? Click No and ask IT (see below).

Check it

bimai bridge status civil3d      # installed version, update available, running or not

In Civil 3D, type BIMAIBRIDGE: it shows running at http://127.0.0.1:27184/mcp. The bridge starts together with Civil 3D, so your team can use it whenever Civil 3D is open with a drawing.

Updates and removal

bimai bridge install civil3d     # installs the newer version over the old one
bimai bridge uninstall civil3d   # removes it (Windows asks permission again)
bimai disconnect civil3d         # removes it from your project

For IT departments

The bridge is a standard Autodesk plug-in bundle. To deploy it to many PCs (Intune, SCCM or a login script), download bimai-civil3d-bridge.zip from the releases, check its SHA-256 against SHA256SUMS.txt, and run as administrator or SYSTEM:

powershell -ExecutionPolicy Bypass -File .\install.ps1

It copies bimai-civil3d.bundle to C:\Program Files\Autodesk\ApplicationPlugins and nothing else. Users then only run bimai connect civil3d. A user can also install from a zip they were given: bimai bridge install civil3d --from bimai-civil3d-bridge.zip.

Troubleshooting

You seeDo this
BIMAIBRIDGE is an unknown commandThe bundle isn't loaded. Run bimai bridge status civil3d; check you use Civil 3D 2025, 2026 or 2027 (not plain AutoCAD), and restart Civil 3D after installing.
"the Windows permission prompt was declined"Run bimai connect civil3d again and click Yes, or ask IT to install it (see above).
"Couldn't download the bridge"Your network or proxy blocks GitHub downloads. Ask IT for the zip and use bimai bridge install civil3d --from <zip>.
"NOT running · port 27184 is already in use"Another Civil 3D (or another program) uses the port. Close it, or set the environment variable BIMAI_CIVIL3D_PORT to another port before starting Civil 3D, and connect with bimai connect civil3d --port <port>.
"Civil 3D is busy"Finish or cancel the command you're in (Esc), then ask again.
"No drawing is open"Open a drawing. The bridge reads the active drawing.
"did not respond within 30 seconds"A dialog box is open, or Civil 3D is doing something long. Close the dialog and try again.
Claude Code shows the server as failedCivil 3D must be running for the bridge to answer.

The bridge keeps a log at %LOCALAPPDATA%\bimai\civil3d-bridge.log: start-up, errors, and which tool ran for how long. It never contains drawing contents.

Test checklist

Please run this once on your machine and report the results (a GitHub issue is fine):

  1. BIMAIBRIDGE says "running" and shows your Civil 3D version in the log.
  2. In Claude Code: "Use get_drawing". Units and coordinate system match the drawing settings.
  3. "List the alignments", then "profile elevations of <alignment> every 20 m". Compare two values with Civil 3D's own profile view.
  4. "Surface elevations of <surface> at <a point inside> and <a point outside>". The second is reported as outside.
  5. Start a command (for example LINE) and ask something: the answer is "Civil 3D is busy". Press Esc and ask again: it works.
  6. "List the corridors" and "get pipe network <name>" on a drawing that has them.
  7. Close Civil 3D: Claude Code reports the server as unavailable, and nothing hangs.

Remove

powershell -ExecutionPolicy Bypass -File .\uninstall.ps1    # as administrator
bimai disconnect civil3d                                     # in your project

For developers

The source is in bridges/civil3d/: a protocol library with a loopback HTTP server and MCP (tested on every platform), the add-in (net8.0-windows for Civil 3D 2025–2026, net10.0-windows for 2027, compiled against Autodesk's AutoCAD.NET and Civil3D.NET NuGet packages), the bundle manifest, and a development server with sample data for testing AI clients without Civil 3D. The server speaks both MCP eras: the stateless 2026-07-28 protocol (which Claude Code uses) and the older initialize handshake.

Connections

Connect your team to Autodesk's MCP servers with one command, and sign in without ever handling a key.

Your BEP becomes the rules

How bimai reads the BIM execution plan and turns it into the project's configuration.

On this page

What it can doSafe by designInstallWhy Windows asks for permissionCheck itUpdates and removalFor IT departmentsTroubleshootingTest checklistRemoveFor developers