What Is an ASMX File?

Open ASP.NET web service files with Visual Studio

By
Tim Fisher
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Tim Fisher
Senior Vice President & Group General Manager, Tech & Sustainability
  • Emporia State University
Tim Fisher has more than 30 years' of professional technology experience. He's been writing about tech for more than two decades and serves as the SVP and General Manager of Lifewire.
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Updated on August 15, 2023

What to Know

  • An ASMX file is an ASP.NET web service file.
  • Open one with Visual Studio.
  • Convert to other formats with that same program.

This article explains what an ASMX file is and how to open or convert one. We'll also look at what to do if you downloaded one by accident.

What Is an ASMX File?

An abbreviation for Active Server Method File, a file with the ASMX file extension is an ASP.NET web service 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

These files are 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 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.

Renaming the file extension like that is not the same as converting the file, and it's not typically recommended to do that except for very specific situations like this where the file simply downloaded with the wrong file extension.

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.

To generate a WSDL file from the ASMX file, append ?WSDL to the end of the web service URL. See this Stack Overflow thread for more on how that works.

Still Can't Open It?

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

If it doesn't show "ASMX" after the file name for your specific file, you'll need to research it again to learn about the program you need on your device to open or convert it.

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. You can't open an ASM file with an ASMX program, or vice versa.

Or maybe you have an ASP file that only works with an Adobe program. SMX is similar; one use for this file is as a SourceMod plug-in.

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