TFS Aggregator is a extension for Team Foundation Server (TFS) and Visual Studio Team Services (VSTS)
that enables running custom script when Work Items change, allowing dynamic calculation of field values in TFS and more.
You can use the Server Plugin, for TFS 2013 update 2 up to TFS 2017 RTM,
or the Web Service version, for VSTS or TFS 2015 and later.
The Web Service version is still in beta.
TFS Server API changed frequently in the past: the Server Plugin contains specific checks for the TFS version.
TFS Aggregator Server Plugin binaries will work only with a specific TFS version.