Post updated 2 November 2021 with the latest links
Revit Lookup is a free, open-source add-in for Revit, which you can use to explore the Revit API.
You will find it invaluable if you are using Dynamo or pyRevit, and also if you are using my Revit Add-in, PropertyWizard.
In this post, I am going to explain how to download and install Revit Lookup, and then in future posts I’ll explain how to get started with Revit Lookup, how to use it in Dynamo and pyRevit, and how to use Revit Lookup with PropertyWizard.
How to download Revit Lookup
The Revit Lookup team have just put in place a new continuous integration system, which means they build an installer for the latest release of Revit Lookup automatically, every time they update the code.
The Revit Lookup homepage has an installation section here:
https://github.com/jeremytammik/RevitLookup#installation

As this says, follow the link to the GitHub Actions page:
https://github.com/jeremytammik/RevitLookup/actions/workflows/CreatePackage.yml
The Actions page shows a series of workflows – each workflow was triggered by a check-in of new code. The successful workflows have a green checkmark:

Choose the most recent successful workflow, and click through to that workflow’s page.
On the workflow page, scroll down to the Artifacts section:

Click on the RevitLookup artifact to download the zip file. You will need to be logged-in to GitHub to do this. If you are not logged-in, there will not appear to be anything clickable!
Once you have downloaded the zip file, unzip it and run the msi installer. When you restart Revit, you should find the Revit Lookup button on the Add-Ins tab of the ribbon:

Once you have installed Revit Lookup, go to this post for details on how to get started, or carry on reading here for more background on Revit Lookup and how to install it for other versions of Revit.
Revit Lookup background
This section has more background on Revit Lookup, and details of alternative ways to download and install it.
Revit Lookup is an open source add-in for Revit, maintained by Jeremy Tammick of Autodesk, on GitHub:

Other ways to install Revit Lookup
Since Revit Lookup is open-source, you can download the source code from GitHub and compile it yourself.
There are also compiled builds available at Lookup Builds. These don’t come with an installer, so you have to install them manually.

The ‘Key’ column shows you which version of Revit the build applies to. Each build is stored as a compressed 7zip file, so you will need a copy of 7zip to unpack them.

Within each build package there are three files:
- RevitLookup.dll, which is the compiled code of the add-in
- RevitLookup.addin, which is the ‘manifest’ file for the add-in
- RevitLookup.pdb, which is a debug file
To install Revit Lookup, place the three files for each Revit version into the relevant Addins folder on your computer:
C:\ProgramData\Autodesk\Revit\Addins\<RevitVersion>
That’s all for this post: Next, you could have a look at the post on Getting Started in Revit Lookup, or on how to use Revit Lookup with PropertyWizard.