As a curious or hands-on small business owner, you might wonder what all those XML files are in your website’s structure as you look to do some backup, check your sitemap, or customize your configuration files.
These powerful little files are the invisible workhorses of your digital business—transmitting order data from your ecommerce store to accounting software, enabling bulk product uploads, exporting customer or sales info, and configuring app and website settings on the fly.
Once you understand what XML files do and how they work, you’ll have a clearer picture of the technology that powers your online business. Here’s more on what these files do, their two key components, and how to properly open one.
What is an XML file?
XML stands for Extensible Markup Language. Documents written in XML format structure and store data so that it’s easy for both humans and machines (like web servers) to read.
The format was initially developed by the World Wide Web Consortium in the late 1990s to standardize how data is exchanged on the internet. Before that, different software platforms (like SAP, QuickBooks, or Microsoft Office) all used their own file formats. The nascent web needed a way for all these disparate platforms to talk to each other and exchange information, and the solution was the XML file.
Here’s a simple example of what an XML file might look like:
<note>
<to>Tove</to>
<from>Jani</from>
<heading>Reminder</heading>
<body>Don’t forget me this weekend!</body>
</note>
If this XML file were used in an internal messaging feature or a customer relationship management notification system, for example, it would tell the software who the message is for, who sent it, the subject, and the message content.
Each piece of information is enclosed in XML tags like <to> or <body> that define the meaning of the data they contain. Think of these tags like quotation marks in a dialogue. The slash in closing tags (e.g., </to>) signals the end of each element, and the entire XML code is enclosed in <note></note>, indicating a complete, self-contained entry.
XML vs. HTML
While they’re both markup languages, HTML and XML perform different tasks. HTML (Hypertext Markup Language) displays content in web browsers, focusing on how information looks. XML, on the other hand, is designed for storing and transporting data—not for displaying it. Put simply, HTML presents data to users, while XML stores data and is more about structure and meaning.
HTML uses predefined tags, like <p> for paragraphs or <image> for images, to control the layout and appearance of content on a web page. Unlike HTML tags, XML lets you—or your development team—define custom tags based on your own data (like <invoice> or <customer>), making it very flexible for a range of applications.
What are XML files used for?
Extensible Markup Language files power much of the behind-the-scenes work in modern business systems. Typical examples include:
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Data transfer. You can use XML to export a product catalog from Shopify to upload into Google Merchant Center for Shopping ads.
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Web applications. A restaurant’s online ordering app could use XML to store customer information—like delivery addresses and favorite meals.
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Data type definitions. An XML file using an XML schema can define what kind of info your accounting system expects when importing invoice files (structured as an XML data file). This helps catch data-entry mistakes early on.
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System configuration. Plug-ins like WooCommerce store their settings (like currency, shipping zones, etc.) in an XML file, making it easy to backup or restore the data structure if you move to a new site.
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Content feeds. RSS—used to push new podcasts or blog posts out to apps like Apple Podcasts or Feedly—is an XML file. It automates the process, so you don’t have to manually update each platform every time you publish something new.
Components of an XML file
Understanding the required structure of an XML file starts with breaking down its basic components. Every XML file is made up of elements, and many include attributes—both of which help organize the content and describe the data types you’re working with. Here’s what you need to know about elements and attributes:
Elements
XML elements are the main building blocks of XML file markup language. They start with an opening tag, (like <name>), contain content (like “John Smith”), and end with a closing tag that includes a forward slash (</name>):
<name>John Smith</name>
XML also supports nested elements, known as child elements, which can help define clear relationships and structure within the data. This is one of the features that makes XML so useful. For example, the following XML contains a top-level <order> element, which includes two <item> elements, each with its own nested elements:
<order>
<customer>Jane Doe</customer>
<items>
<item>
<name>Notebook</name>
<quantity>2</quantity>
</item>
<item>
<name>Pen</name>
<quantity>5</quantity>
</item>
</items>
</order>
Each line in the XML shows the document structure and how elements are nested, making it easier for humans to see which pieces of data belong together. In the above example, you can see that the <order> element contains both <customer> and <items>, while the individual <item> entries are nested within <items>. Each <item> includes its own <name> and <quantity>.
While XML doesn’t require indentation, it’s a best practice—it improves readability and helps your team quickly understand the file’s structure.
Attributes
Attributes in XML are optional, but they add extra details about an element. You’ll find them within the opening tag, with their values enclosed in quotes. For example:
<product id="123" category="books">The Hobbit</product>
The opening tag is <product> with the attributes id="123" and category="books". The Hobbit is the XML content, and </product> is the end tag.
You can assign multiple attributes to any element in an XML file—as long as each attribute has a unique name within that element and you place all attributes inside the opening tag, separated by spaces. So, for the example above, you might have:
<product id="123" category="books" author="JRR Tolkien" genre="fantasy”>The Hobbit</product>
Attributes are best for short, simple values like IDs, categories, or flags (simple data types), and good for metadata, but not great for storing long or complex information. If your attribute is very long, consider making it a separate element (a cleaner approach in most cases), instead. For example, this is a good use of attributes:
<product id="1234" category="books" available="true" />
But this is not recommended:
<product description="This beautifully written novel explores themes of loss, love, and redemption through the lens of a small-town librarian..." />
Instead, use an element for the longer content:
<product id="1234" category="books" available="true">
<description>
This beautifully written novel explores themes of loss, love, and redemption through the lens of a small-town librarian...
</description>
</product>
This structure is cleaner, easier to manage, and scales better—especially for longer or multi-line text.
What is XML schema?
An XML Schema, or XSD (XML Schema Definition) file, defines the XML syntax rules for what’s allowed in an XML file. Think of it as a blueprint—similar to the guidelines you might receive from the IRS for filling out a form—specifying exactly what data is required, where it should go, and in what format. This ensures consistency and helps software validate that the XML file is structured correctly.
You typically create XSD files for each type of XML file (like invoice files, customer data files, configuration files, etc.), not for every individual XML document. For example, you might have an XML schema that defines the structure for all invoice files, while a second one defines customer data or product feeds. This way, if you generate 20 invoice XML files, they can all follow the same set of rules without needing 20 separate schema files.
As a quick example, if your XML file contains <price>19.99</price> and your schema defines “price” as a decimal, entering something like “nineteen dollars and ninety-nine cents” would break the rules and invalidate the file. Schema validation helps ensure data integrity and catches formatting errors before the XML is processed by your software.
How to open an XML file?
You don’t need specialized software to open and read XML files. You can use a text editor or a web browser. Here’s how:
Opening an XML file with a text editor
Choose a text editor when you need to manually edit, review the document structure, inspect or troubleshoot the file, view raw data without formatting, or work offline with local files.
Avoid using word processors like Microsoft Word, as these can add hidden formatting that breaks the file. Stick with tools that save in plain text format, like Notepad or TextEdit—and make sure you choose the plain text format when you create the file.
On a Mac, simply right-click on the .xml file (a common XML file extension), then choose Open With > TextEdit or BBeddit, or whichever text editing program you prefer.
Windows works similarly—just right-click the XML file, then choose Open With > Notepad or VS Code, edit the file directly within the app, and then save it back to your web server via FTP or a web-based interface.
Opening an XML file with an online browser
If you just need a quick look at an XML file’s contents, any web browser can open and display it—making it a convenient option for simply viewing a file someone sends you.
Simply right-click the XML file, then choose Open with > Chrome, Firefox, Edge, or your browser of choice. While browsers are great for viewing XML, they can’t edit files or validate them against a schema—you’ll need a specialized tool or code editor for those tasks.
XML file FAQ
What is an XML file used for?
XML files store and exchange structured data between software systems, facilitating tasks like synching product listings, exporting reports, or configuring app settings.
What program opens an XML file?
Text editors and web browsers can both open .XML files, but while web browsers let you view the file, only text editors allow you to make changes. Spreadsheet apps like Excel and code editors, like VS Code or Sublime Text can also open XML files.
Is XML an Excel file?
No. Excel can open an XML file and create a readable table for all the data in the file so you can work with it in a familiar environment. When you’re done, you can export back to XML, as long as it’s mapped to an XML Scheme file.
