What are the project GUIDs in a Visual Studio solution file used for?
The first GUID is the project type. Project type GUIDs can be found here:
http://www.codeproject.com/Reference/720512/List-of-Visual-Studio-Project-Type-GUIDs
From the link:
There isn't an easy way to change the type of a project in Visual Studio project once it is created; for example changing a C# Class Library into a Portable Class Library (PCL). Knowing these GUIDs will allow you to edit project files like .csproj and .vbproj to easily change a project type in cases where Visual Studio will not allow using the GUI.
By description/project type:
+------------------------------------------------+----------------------------------------+
| Project Type | GUID
+------------------------------------------------+----------------------------------------+
| .NET Core | {9A19103F-16F7-4668-BE54-9A1E7A4F7556} |
| ASP.NET 5 | {8BB2217D-0F2D-49D1-97BC-3654ED321F3B} |
| ASP.NET MVC 1 | {603C0E0B-DB56-11DC-BE95-000D561079B0} |
| ASP.NET MVC 2 | {F85E285D-A4E0-4152-9332-AB1D724D3325} |
| ASP.NET MVC 3 | {E53F8FEA-EAE0-44A6-8774-FFD645390401} |
| ASP.NET MVC 4 | {E3E379DF-F4C6-4180-9B81-6769533ABE47} |
| ASP.NET MVC 5 | {349C5851-65DF-11DA-9384-00065B846F21} |
| C# | {FAE04EC0-301F-11D3-BF4B-00C04F79EFBC} |
| C++ | {8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942} |
| Database | {A9ACE9BB-CECE-4E62-9AA4-C7E7C5BD2124} |
| Database (other project types) | {4F174C21-8C12-11D0-8340-0000F80270F8} |
| Deployment Cab | {3EA9E505-35AC-4774-B492-AD1749C4943A} |
| Deployment Merge Module | {06A35CCD-C46D-44D5-987B-CF40FF872267} |
| Deployment Setup | {978C614F-708E-4E1A-B201-565925725DBA} |
| Deployment Smart Device Cab | {AB322303-2255-48EF-A496-5904EB18DA55} |
| Distributed System | {F135691A-BF7E-435D-8960-F99683D2D49C} |
| Dynamics 2012 AX C# in AOT | {BF6F8E12-879D-49E7-ADF0-5503146B24B8} |
| F# | {F2A71F9B-5D33-465A-A702-920D77279786} |
| J# | {E6FDF86B-F3D1-11D4-8576-0002A516ECE8} |
| Legacy (2003) Smart Device (C#) | {20D4826A-C6FA-45DB-90F4-C717570B9F32} |
| Legacy (2003) Smart Device (VB.NET) | {CB4CE8C6-1BDB-4DC7-A4D3-65A1999772F8} |
| Micro Framework | {b69e3092-b931-443c-abe7-7e7b65f2a37f} |
| Model-View-Controller v2 (MVC 2) | {F85E285D-A4E0-4152-9332-AB1D724D3325} |
| Model-View-Controller v3 (MVC 3) | {E53F8FEA-EAE0-44A6-8774-FFD645390401} |
| Model-View-Controller v4 (MVC 4) | {E3E379DF-F4C6-4180-9B81-6769533ABE47} |
| Model-View-Controller v5 (MVC 5) | {349C5851-65DF-11DA-9384-00065B846F21} |
| Mono for Android | {EFBA0AD7-5A72-4C68-AF49-83D382785DCF} |
| MonoTouch | {6BC8ED88-2882-458C-8E55-DFD12B67127B} |
| MonoTouch Binding | {F5B4F3BC-B597-4E2B-B552-EF5D8A32436F} |
| Portable Class Library | {786C830F-07A1-408B-BD7F-6EE04809D6DB} |
| Project Folders | {66A26720-8FB5-11D2-AA7E-00C04F688DDE} |
| Service Fabric Application (.sfproj) | {A07B5EB6-E848-4116-A8D0-A826331D98C6} |
| SharePoint (C#) | {593B0543-81F6-4436-BA1E-4747859CAAE2} |
| SharePoint (VB.NET) | {EC05E597-79D4-47f3-ADA0-324C4F7C7484} |
| SharePoint Workflow | {F8810EC1-6754-47FC-A15F-DFABD2E3FA90} |
| Silverlight | {A1591282-1198-4647-A2B1-27E5FF5F6F3B} |
| Smart Device (C#) | {4D628B5B-2FBC-4AA6-8C16-197242AEB884} |
| Smart Device (VB.NET) | {68B1623D-7FB9-47D8-8664-7ECEA3297D4F} |
| Solution Folder | {2150E333-8FDC-42A3-9474-1A3956D46DE8} |
| Test | {3AC096D0-A1C2-E12C-1390-A8335801FDAB} |
| Universal Windows Class Library | {A5A43C5B-DE2A-4C0C-9213-0A381AF9435A} |
| VB.NET | {F184B08F-C81C-45F6-A57F-5ABD9991F28F} |
| Visual Database Tools | {C252FEB5-A946-4202-B1D4-9916A0590387} |
| Visual Studio 2015 Installer Project Extension | {54435603-DBB4-11D2-8724-00A0C9A8B90C} |
| Visual Studio Tools for Applications (VSTA) | {A860303F-1F3F-4691-B57E-529FC101A107} |
| Visual Studio Tools for Office (VSTO) | {BAA0C2D2-18E2-41B9-852F-F413020CAA33} |
| Web Application | {349C5851-65DF-11DA-9384-00065B846F21} |
| Web Site | {E24C65DC-7377-472B-9ABA-BC803B73C61A} |
| Windows (C#) | {FAE04EC0-301F-11D3-BF4B-00C04F79EFBC} |
| Windows (VB.NET) | {F184B08F-C81C-45F6-A57F-5ABD9991F28F} |
| Windows (Visual C++) | {8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942} |
| Windows Communication Foundation (WCF) | {3D9AD99F-2412-4246-B90B-4EAA41C64699} |
| Windows Phone 8/8.1 Blank/Hub/Webview App | {76F1466A-8B6D-4E39-A767-685A06062A39} |
| Windows Phone 8/8.1 App (C#) | {C089C8C0-30E0-4E22-80C0-CE093F111A43} |
| Windows Phone 8/8.1 App (VB.NET) | {DB03555F-0C8B-43BE-9FF9-57896B3C5E56} |
| Windows Presentation Foundation (WPF) | {60DC8134-EBA5-43B8-BCC9-BB4BC16C2548} |
| Windows Store (Metro) Apps & Components | {BC8A1FFA-BEE3-4634-8014-F334798102B3} |
| Workflow (C#) | {14822709-B5A1-4724-98CA-57A101D1B079} |
| Workflow (VB.NET) | {D59BE175-2ED0-4C54-BE3D-CDAA9F3214C8} |
| Workflow Foundation | {32F31D43-81CC-4C15-9DE6-3FC5453562B6} |
| Xamarin.Android | {EFBA0AD7-5A72-4C68-AF49-83D382785DCF} |
| Xamarin.iOS | {6BC8ED88-2882-458C-8E55-DFD12B67127B} |
| XNA (Windows) | {6D335F3A-9D43-41b4-9D22-F6F17C4BE596} |
| XNA (XBox) | {2DF5C3F4-5A5F-47a9-8E94-23B4456F55E2} |
| XNA (Zune) | {D399B71A-8929-442a-A9AC-8BEC78BB2433} |
+------------------------------------------------+----------------------------------------+
By GUID:
+------------------------------------------------+----------------------------------------+
| Project Type | GUID
+------------------------------------------------+----------------------------------------+
| Deployment Merge Module | {06A35CCD-C46D-44D5-987B-CF40FF872267} |
| Workflow (C#) | {14822709-B5A1-4724-98CA-57A101D1B079} |
| Legacy (2003) Smart Device (C#) | {20D4826A-C6FA-45DB-90F4-C717570B9F32} |
| Solution Folder | {2150E333-8FDC-42A3-9474-1A3956D46DE8} |
| XNA (XBox) | {2DF5C3F4-5A5F-47a9-8E94-23B4456F55E2} |
| Workflow Foundation | {32F31D43-81CC-4C15-9DE6-3FC5453562B6} |
| Web Application (incl. MVC 5) | {349C5851-65DF-11DA-9384-00065B846F21} |
| Test | {3AC096D0-A1C2-E12C-1390-A8335801FDAB} |
| Windows Communication Foundation (WCF) | {3D9AD99F-2412-4246-B90B-4EAA41C64699} |
| Deployment Cab | {3EA9E505-35AC-4774-B492-AD1749C4943A} |
| Smart Device (C#) | {4D628B5B-2FBC-4AA6-8C16-197242AEB884} |
| Database (other project types) | {4F174C21-8C12-11D0-8340-0000F80270F8} |
| Visual Studio 2015 Installer Project Extension | {54435603-DBB4-11D2-8724-00A0C9A8B90C} |
| SharePoint (C#) | {593B0543-81F6-4436-BA1E-4747859CAAE2} |
| ASP.NET MVC 1.0 | {603C0E0B-DB56-11DC-BE95-000D561079B0} |
| Windows Presentation Foundation (WPF) | {60DC8134-EBA5-43B8-BCC9-BB4BC16C2548} |
| Smart Device (VB.NET) | {68B1623D-7FB9-47D8-8664-7ECEA3297D4F} |
| Project Folders | {66A26720-8FB5-11D2-AA7E-00C04F688DDE} |
| MonoTouch | {6BC8ED88-2882-458C-8E55-DFD12B67127B} |
| XNA (Windows) | {6D335F3A-9D43-41b4-9D22-F6F17C4BE596} |
| Windows Phone 8/8.1 Blank/Hub/Webview App | {76F1466A-8B6D-4E39-A767-685A06062A39} |
| Portable Class Library | {786C830F-07A1-408B-BD7F-6EE04809D6DB} |
| ASP.NET 5 | {8BB2217D-0F2D-49D1-97BC-3654ED321F3B} |
| C++ | {8BC9CEB8-8B4A-11D0-8D11-00A0C91BC942} |
| Deployment Setup | {978C614F-708E-4E1A-B201-565925725DBA} |
| .NET Core | {9A19103F-16F7-4668-BE54-9A1E7A4F7556} |
| Service Fabric Application (.sfproj) | {A07B5EB6-E848-4116-A8D0-A826331D98C6} |
| Silverlight | {A1591282-1198-4647-A2B1-27E5FF5F6F3B} |
| Universal Windows Class Library | {A5A43C5B-DE2A-4C0C-9213-0A381AF9435A} |
| Visual Studio Tools for Applications (VSTA) | {A860303F-1F3F-4691-B57E-529FC101A107} |
| Database | {A9ACE9BB-CECE-4E62-9AA4-C7E7C5BD2124} |
| Deployment Smart Device Cab | {AB322303-2255-48EF-A496-5904EB18DA55} |
| Micro Framework | {B69E3092-B931-443C-ABE7-7E7B65F2A37F} |
| Visual Studio Tools for Office (VSTO) | {BAA0C2D2-18E2-41B9-852F-F413020CAA33} |
| Windows Store Apps (Metro Apps) | {BC8A1FFA-BEE3-4634-8014-F334798102B3} |
| C# in Dynamics 2012 AX AOT | {BF6F8E12-879D-49E7-ADF0-5503146B24B8} |
| Windows Phone 8/8.1 App (C#) | {C089C8C0-30E0-4E22-80C0-CE093F111A43} |
| Visual Database Tools | {C252FEB5-A946-4202-B1D4-9916A0590387} |
| Legacy (2003) Smart Device (VB.NET) | {CB4CE8C6-1BDB-4DC7-A4D3-65A1999772F8} |
| XNA (Zune) | {D399B71A-8929-442a-A9AC-8BEC78BB2433} |
| Workflow (VB.NET) | {D59BE175-2ED0-4C54-BE3D-CDAA9F3214C8} |
| Windows Phone 8/8.1 App (VB.NET) | {DB03555F-0C8B-43BE-9FF9-57896B3C5E56} |
| Web Site | {E24C65DC-7377-472B-9ABA-BC803B73C61A} |
| ASP.NET MVC 4.0 | {E3E379DF-F4C6-4180-9B81-6769533ABE47} |
| ASP.NET MVC 3.0 | {E53F8FEA-EAE0-44A6-8774-FFD645390401} |
| J# | {E6FDF86B-F3D1-11D4-8576-0002A516ECE8} |
| SharePoint (VB.NET) | {EC05E597-79D4-47f3-ADA0-324C4F7C7484} |
| Xamarin.Android / Mono for Android | {EFBA0AD7-5A72-4C68-AF49-83D382785DCF} |
| Distributed System | {F135691A-BF7E-435D-8960-F99683D2D49C} |
| VB.NET | {F184B08F-C81C-45F6-A57F-5ABD9991F28F} |
| F# | {F2A71F9B-5D33-465A-A702-920D77279786} |
| MonoTouch Binding | {F5B4F3BC-B597-4E2B-B552-EF5D8A32436F} |
| ASP.NET MVC 2.0 | {F85E285D-A4E0-4152-9332-AB1D724D3325} |
| SharePoint Workflow | {F8810EC1-6754-47FC-A15F-DFABD2E3FA90} |
| C# | {FAE04EC0-301F-11D3-BF4B-00C04F79EFBC} |
+------------------------------------------------+----------------------------------------+
Notes: You will find these properties as a
<ProjectTypeGuids>element in the project file, not to be confused with<ProjectGuid>which is a unique identifier for your project.
Some GUIDs are used in combination. For example,
<ProjectTypeGuids>{EFBA0AD7-5A72-4C68-AF49-83D382785DCF};{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}</ProjectTypeGuids>describes a Xamarin.Android library in C#.
Project persistence block in a solution file has the following format:
Project("{project type GUID}") = "<Project name>", "<project file location>",
"{<Unique project GUID>}"
EndProject
So it's expected that first GUID is non-unique, it uniquely identifies Visual Studio package that handles this type of projects.
The GUID you posted is interesting - it looks like mangled C# project GUID, which is FAE04EC0-301F-11D3-BF4B-00C04F79EFBC. Did you change it yourself or is it a posting issue (e.g. you are using right-to-left locale such as Hebrew or Arabic).