The Developer Toolkit is a set of Microsoft Visual Studio Integration tools, focused on accelerating the development of custom code for Microsoft Dynamics 365(CRM).
Below URL can be used to download:
Microsoft Developer toolkit for Dynamics 365 / CRM has traditionally lagged behind Visual Studio in terms of releases, but with a few tweaks, it’s possible to get it up and running.
Step 1 – Download the VSIX for Dynamics 365.
This can be downloaded from here. Save it somewhere locally.

Step 2 – Extract the VSIX.
The VSIX is an archive. We need to update a file in there to get it to install. My tool of choice for doing this is 7zip. Right click and extract to a subfolder.

Step 3 – Update the VSIX Manifest
With a text editor, update the extension.vsixmanifest file. The existing VSIX will only work up to Visual Studio 2015 (14.0), so you need to update the references from version 14 to version 15. Once complete as shown below, save the file.

Step 4 – Install the VSIX
Because the VSIX was compiled by and for VS 2015, you will get a warning when installing, but it should still install successfully. We won’t be able to get rid of this warning, but just click OK, close and Restart Visual Studio.

Step 5 – Set your Dynamics 365 SDK Paths in Visual Studio
If you haven’t already installed the SDK, download and extract it now. Then go to Tools -> Options -> Dynamics 365 Developer Toolkit -> Tool Paths. Set the paths to point to the plugin registration tool folder and bin folder where you extracted your SDK.

Once installed.
You can create New project selecting the MS dynamics 365 tool. Create a new solution which will get create in CRM as a solution.
Benefit of having toolkit is it gives you the base class. It contains all necessary service initalized.
such as:
PluginExecutionContext
OrganizationService
TracingService
Code Samples:
internal LocalPluginContext(IServiceProvider serviceProvider)
{
if (serviceProvider == null)
{
throw new InvalidPluginExecutionException(“serviceProvider”);
}
// Obtain the execution context service from the service provider.
PluginExecutionContext = (IPluginExecutionContext)serviceProvider.GetService(typeof(IPluginExecutionContext));
// Obtain the tracing service from the service provider.
TracingService = (ITracingService)serviceProvider.GetService(typeof(ITracingService));
// Get the notification service from the service provider.
NotificationService = (IServiceEndpointNotificationService)serviceProvider.GetService(typeof(IServiceEndpointNotificationService));
// Obtain the organization factory service from the service provider.
IOrganizationServiceFactory factory = (IOrganizationServiceFactory)serviceProvider.GetService(typeof(IOrganizationServiceFactory));
// Use the factory to generate the organization service.
OrganizationService = factory.CreateOrganizationService(PluginExecutionContext.UserId);
}
Post that it also gives you an entity explorer through which you can select an entity and create new plugin steps.
Once created it will give you all necessary class method to start with custom code.
Code sample:
protected override void ExecuteCrmPlugin(LocalPluginContext localContext)
{
if (localContext == null)
{
throw new InvalidPluginExecutionException(“localContext”);
}
// TODO: Implement your custom Plug-in business logic.
Entity entity = (Entity)localContext.PluginExecutionContext.InputParameters[“Target”];
if (localContext.PluginExecutionContext.MessageName.ToUpper() == “UPDATE”)
{
localContext.OrganizationService.Update(entity);
}
}
Developer toolkit is one of the helpful tool to write and deploy plugins,custom activity and Web resource directly to CRM as solution component.
Thanks.