No executable found matching command "dotnet-ef"

If You get error like this:
No executable found matching command "dotnet-ef"
This is solution.

1. Check if You have csproj inside directory of command execution

2. Check if there is a reference to the "watcher" tool in the project file (csproj)

<ItemGroup>
    <DotNetCliToolReference Include="Microsoft.EntityFrameworkCore.Tools.DotNet" Version="2.0.0"/>
</ItemGroup>

and then execute

dotnet restore