Complementing this answer https://stackoverflow.com/a/2328668/6998967

There are definitions of GUIDs in the .NET codebase:

• https://github.com/dotnet/dotnet/blob/408e19901b7cb158c36d16e378334888b590291d/src/source-build-reference-packages/src/externalPackages/src/vs-solutionpersistence/src/Microsoft.VisualStudio.SolutionPersistence/Model/ProjectTypeTable.BuiltInTypes.cs#L39

  GUID	Description	Extension
  2150E333-8FDC-42A3-9474-1A3956D46DE8	Folder	NA
  9A19103F-16F7-4668-BE54-9A1E7A4F7556	Common C#	NA
  778DAE3C-4631-46EA-AA77-85C1314464D9	Common VB	NA
  6EC3EE1D-3C4E-46DD-8F32-0CC8E7565705	Common F#	NA
  FAE04EC0-301F-11D3-BF4B-00C04F79EFBC	C#	.csproj
  F184B08F-C81C-45F6-A57F-5ABD9991F28F	VB	.vbproj
  F2A71F9B-5D33-465A-A702-920D77279786	F#	.fsproj
  D954291E-2A0B-460D-934E-DC6B0785DB48	Shared	.shproj
  E24C65DC-7377-472B-9ABA-BC803B73C61A	Website	.webproj
  8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942	VC	.vcxproj
  8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942	VC (shared items)	.vcxitems
  911E67C6-3D85-4FCE-B560-20A9C3E3FF48	Exe	.exe
  54A90642-561A-4BB1-A94E-469ADEE60C69	Javascript	.esproj
  9092AA53-FB77-4645-B42D-1CCCA6BD08BD	Node.js	.njsproj
  151D2E53-A2C4-4D7D-83FE-D05416EBD58E	Deploy	.deployproj
  54435603-DBB4-11D2-8724-00A0C9A8B90C	Installer	.vsproj
  930C7802-8A8C-48F9-8165-68863BCCD9DD	Wix	.wixproj
  00D1A9C2-B5F0-4AF3-8072-F6C62B433612	SQL	.sqlproj
  0C603C2C-620A-423B-A800-4F3E2F6281F1	U-SQL-DB	.usqldbproj
  182E2583-ECAD-465B-BB50-91101D7C24CE	U-SQL	.usqlproj
  A07B5EB6-E848-4116-A8D0-A826331D98C6	Fabric	.sfproj
  CC5FD16D-436D-48AD-A40C-5A424C6E3E79	Cloud Computing	.ccproj
  E53339B2-1760-4266-BCC7-CA923CBCF16C	Docker	.dcproj

There are other GUIDs in the following files:

• https://github.com/dotnet/dotnet/blob/408e19901b7cb158c36d16e378334888b590291d/src/nuget-client/src/NuGet.Clients/NuGet.VisualStudio.Common/VsProjectTypes.cs#L9
• https://github.com/dotnet/dotnet/blob/408e19901b7cb158c36d16e378334888b590291d/src/roslyn/src/VisualStudio/Core/Def/Guids.cs#L12