What is a Revit plugin? How add-ins work, and when you need one

A plugin has two parts. The first is a .NET assembly, the DLL, which holds the code. The second is an .addin manifest, a short XML file naming the DLL's path, the class to run, and a unique ID (a GUID). At startup Revit reads manifests from two folders: one shared by all users under ProgramData, and one for the current user under AppData, each with a subfolder named for the Revit version year.

The code implements one of two Revit API interfaces. IExternalCommand is a single command: press the button, it runs, it finishes. IExternalApplication loads when Revit opens and can build its own ribbon tab and panels, or respond to events such as a file opening or saving. Most complete plugins use both, an application that builds the ribbon and several commands behind its buttons.

Every change an add-in makes to the model happens inside a transaction, the same way a change made by hand does. So the add-in's changes can be undone, and they land in the model's history. The structure of a Revit API project is covered in more depth in Revit API development.

These words name one thing. Autodesk's Revit API documentation says add-in. The Autodesk App Store calls them apps. Users and vendors mostly say plugin or add-on.

The real difference isn't the name, it's how the thing is built. A compiled C# add-in, a Dynamo script and a macro inside Revit can all automate the same task. They differ a lot in how they're installed, maintained and rolled out to a team.

There are four common ways to add a capability to Revit:

• Compiled add-in: a DLL and an .addin manifest, usually C#. Fastest to run, full user interface, ships with an installer. Needs a developer to build.
• Dynamo script: visual programming by wiring nodes, run inside Dynamo or through Dynamo Player. Good for repeated tasks inside one team and for quick prototypes. Depends on the Dynamo version and the packages installed.
• pyRevit: a free, open-source add-in that runs Python scripts as ribbon buttons. Quick for small tools, and it ships with a set of ready-made tools of its own.
• Macro: code written and run through Revit's Macro Manager. Enough for a small job in one file or for one user. Hard to distribute and maintain across a team.

Rough rule: if one person does the task once a week, a Dynamo script or a pyRevit button is usually enough. If the whole office relies on the tool every day, needs a proper interface, or has to run across several Revit versions, a compiled add-in is the better fit. Custom Dynamo script development draws that line in more detail.

Commercial and free plugins mostly fall into a few groups: rendering and live visualisation, model quality and warning review, sheet management and PDF or DWG export, moving data between Revit and Excel, family and library management, and discipline tools for structure and MEP such as system design and rebar.

Custom plugins usually do something that only exists in that form in one office: that office's naming standard, the report format its client asks for, or converting another program's output into native Revit elements. Nobody sells those ready-made, because only one team does them that way.

Most plugins come with an installer that puts the files in the right Addins folder. After installing, close Revit and open it again. If the add-in isn't digitally signed, Revit shows a security prompt at startup asking whether to always load it, load it once, or not load it.

Each Revit version has its own folder, and a plugin built for Revit 2024 won't necessarily run in 2025. From 2025, the Revit API moved to .NET 8, and add-ins written for .NET Framework have to be rebuilt. Before an office upgrades Revit, list the plugins the team depends on and check each one.

To remove a plugin, use Windows' installed apps list or the add-in's own uninstaller. If a load error remains afterwards, there's usually an .addin file left behind in one of the Addins folders; delete it. Only install add-ins from a source you can name. A plugin has access to every file Revit opens.

Before commissioning a plugin, check the Autodesk App Store, pyRevit's tools and the Dynamo package library. Plenty of generic jobs, batch renaming, sheet ordering, Excel export, already have a ready-made tool that does the same thing for less. If one of those does your job, you don't need us, or anyone like us.

A custom plugin earns its place when the office's workflow runs on the office's own rules, when several people repeat the task every day, or when a manual error in it has a known cost. Then the tool gets designed around how the team actually works. How that work is priced is in how much Revit plugin development costs, and the service itself is Revit plugin development.