What Is an ASMX File?

How to open, edit, & convert ASMX files

An abbreviation for Active Server Method File, a file with the ASMX file extension is an ASP.NET Web Service Source file.

Unlike ASP.NET web pages that use the .ASPX file extension, ASMX files function as a service that doesn't have a graphical user interface and instead is used to move data and perform other actions behind the scenes.

ASMX files in Windows 10 that open with Microsoft Visual Studio

Be careful to not confuse ASMX and ASCX files. While they might appear similar, they're used for different reasons.

How to Open an ASMX File

ASMX files are files used with ASP.NET programming and can be opened with any program that codes in ASP.NET, like Microsoft's Visual Studio.

You might also be able to use Windows Notepad or another free text editor to open the ASMX file for editing as a text file.

ASMX files aren't intended to be viewed or opened by the browser. If you've downloaded an ASMX file and expected it to contain information (like a document or other saved data), it's likely that something is wrong with the website and instead of generating usable information, it provided this server-side file instead. Try renaming the file to the correct extension as a short term fix.

For example, if when trying to download a document in the PDF format, you instead get one with the .ASMX file extension, just delete the four letters after the period and replace them with .PDF.

If you find that an application on your PC does try to open the ASMX file but it's the wrong application or you'd rather have another installed program open ASMX files, see How to Change the Default Program for a Specific File Extension for making that change in Windows.

How to Convert an ASMX File

You might be able to use Microsoft's program linked above to convert an ASMX file to another format.

Here's some information on migrating ASP.NET Web Services to the Windows Communication Foundation (WCF) platform. This is useful if you need to use .NET 2.0 services under .NET 3.0.

Still Can't Open the File?

If your file doesn't open with the suggestions above, you might be dealing with a completely different format. This might happen if you've misread the file extension. Some files use a similar extension even though the formats are entirely different.

For example, ASM files are just missing the "x" when compared to ASMX files, but they're actually design files used by programs like Autodesk Fusion 360 and Siemens Solid Edge. You can't open an ASM file with an ASMX program, or vice versa.

SMX is similar. Reserved for SmartMusic XML files, you need the SmartMusic program on your computer to open them.