RevitSync

Revit posts a bounding-box snapshot to a local ASP.NET Core API. A React / Three.js page polls that API and draws the same elements. Clicks in the browser enqueue commands. The add-in polls the queue and applies them on Revit's UI thread.

Revit add-in                    ASP.NET Core API                 Browser (React + Three.js)
────────────                    ────────────────                 ──────────────────────────
Export / DocumentChanged
  POST /api/geometry     ──►    latest snapshot in memory  ──►   GET /api/geometry/latest (2s)
                                                                     draw boxes, highlight

Click / drag / delete
  GET /api/commands/next ◄──    per-project command queue  ◄──   POST /api/commands
  ExternalEvent + Transaction

Local demo only. Three processes on one machine (localhost:5245). This is a personal learning project, not production software.

Unofficial, not Autodesk work. Independent portfolio project by Mayur Reddy. Not an Autodesk product. Not affiliated with, endorsed by, or sponsored by Autodesk, Inc. Autodesk and Revit are trademarks of Autodesk, Inc.

Demo

youtube.com/watch?v=9N6vfX0DKNM : Revit on the left, web viewer on the right. Export, selection sync, live DocumentChanged updates, click-to-place boxes.

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What it does

Revit to web

• Export: world-axis bounding boxes from 13 categories in the active view (whole document only if there is no view)
• Auto-sync: DocumentChanged starts a 500 ms debounce, then an ExternalEvent re-exports
• Selection: Idling checks selection every 300 ms. Selected ids ride along on the next snapshot. Viewer outlines them cyan
• Properties: Name, Family, Type, Level, Mark, Comments, Length, Area, Volume, wall/floor offsets, phases, and Workset when the model is workshared
• Colors: one hex color per category

Web to Revit

Command	What happens in Revit
ADD_BOXES	Creates DirectShape boxes in OST_GenericModel, tagged ApplicationId = "RevitSync"
MOVE_ELEMENT	Translates that tagged DirectShape to a new center
DELETE_ELEMENTS	Deletes those tagged DirectShapes only
SELECT_ELEMENTS	Selection.SetElementIds plus ShowElements (zoom). No transaction

Move and delete from the web do not apply to ordinary Revit walls, floors, or families.

Categories exported

Walls, Roofs, Floors, Structural Columns, Structural Framing, Structural Foundation, Windows, Doors, Curtain Wall Panels, Curtain Wall Mullions, Stairs, Ramps, Generic Model.

Limits (exact)

• Geometry is axis-aligned bounding boxes, not meshes, faces, or rooms
• Export with zero primitives does not POST, so the last snapshot stays in the API
• Snapshot and command queue live in process memory. Restart the API and they are gone
• No auth, no TLS on the demo URL, no multi-user, no conflict resolution
• Add-in and viewer hard-code http://localhost:5245
• Viewer poll: 2 s. Add-in command poll: 1.5 s. Not WebSockets
• The API sends ETag. The viewer sends If-None-Match and reuses the last snapshot on 304
• DTOs are copied in the add-in, the API, and TypeScript. There is no shared contract package
• Command handler keeps one Pending slot. A second dequeue before Execute can drop the first command
• Element ids on move/delete/select are parsed with int.TryParse
• Generate Column Grid needs an active crop box and a structural column family
• Add-in project is .NET Framework 4.8 targeting Revit 2026 assemblies. Autodesk's official add-in target for Revit 2025/2026 is .NET 8. If the add-in does not load, check that mismatch first. This repo does not retarget it

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Tech

Process	Stack
Revit add-in	C#, .NET Framework 4.8, Revit API (RevitYear defaults to 2026)
Backend	ASP.NET Core 9, in-memory ConcurrentDictionary / ConcurrentQueue, Swagger
Frontend	React 19, TypeScript, Three.js (React Three Fiber), TanStack Query, Tailwind CSS

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Run it

API and viewer first, then Revit. Everything talks to http://localhost:5245.

1. Backend

cd backend/RevitSync.Api
dotnet run

API: http://localhost:5245 · Swagger: http://localhost:5245/swagger

2. Frontend

cd frontend/revit-sync-frontend
npm install
npm run dev

Viewer: http://127.0.0.1:5173 (Vite is pinned to that host and port). http://localhost:5173 also works.

3. Revit add-in

Needs Autodesk Revit 2026 at C:\Program Files\Autodesk\Revit 2026\ (the .csproj references those RevitAPI.dll / RevitAPIUI.dll files). Other years: set RevitYear in the .csproj and copy into that year's Addins folder.

1. Open revit-addin/RevitSync.Addin/RevitSync.Addin.sln in Visual Studio.
2. Restore NuGet if prompted (Newtonsoft.Json).
3. Build the solution. A post-build step copies RevitSync.Addin.dll, RevitSync.addin, and the ribbon icon into %APPDATA%\Autodesk\Revit\Addins\2026\
4. Restart Revit. The RevitSync panel is on the Add-Ins tab.

Manual install: copy revit-addin/RevitSync.Addin/RevitSync.Addin/RevitSync.addin next to the DLL in that Addins folder. The Assembly path is the DLL file name.

Also needed: .NET 9 SDK for the API, Node.js 18+ for the viewer, Visual Studio 2022+ with .NET desktop development for the 4.8 add-in.

Demo clicks

1. Start API and viewer.
2. Open a Revit model that has walls, floors, or roofs in the active view.
3. Click Export Geometry on the RevitSync ribbon.
4. Open http://127.0.0.1:5173. Orbit / pan / zoom. Click a box for properties.
5. Select in Revit highlights and zooms that element.
6. Select in Revit. The same box goes cyan in the viewer.
7. Click to Place → click the ground plane. A box appears as a DirectShape after the next command poll (~1.5 s) plus the next viewer poll (~2 s).
8. Select a web-created box → drag the transform arrows to move, or Delete.
9. After the first export, model edits re-export through DocumentChanged. Generate Column Grid is an optional helper if you have no model yet (needs crop box + a column family).

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API

Endpoint	Method	What it does
/api/geometry	POST	Store latest snapshot for projectName
/api/geometry/latest	GET	Latest snapshot. Optional ?projectName=. If-None-Match → 304
/api/commands	POST	Enqueue ADD_BOXES, DELETE_ELEMENTS, MOVE_ELEMENT, or SELECT_ELEMENTS
/api/commands/next	GET	Dequeue one command. Optional ?projectName=. 204 if empty

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Checks you can run without Revit

dotnet test backend/RevitSync.Api.Tests/RevitSync.Api.Tests.csproj
cd frontend/revit-sync-frontend && npm run build && npm run lint

The add-in needs Revit assemblies on disk. Visual Studio Build Solution is the check for that project.

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License

MIT © Mayur Reddy

Autodesk and Revit are registered trademarks of Autodesk, Inc. This project is a personal learning exercise and is not an official Autodesk sample or plugin.