What you need to do before converting an XML file
Before you convert an XML file to another format, you need to make sure the file itself is valid — meaning it follows XML rules so the conversion tool can read it without errors. A broken XML file will either fail to convert or produce garbled output in the new format.
The most common problems are unclosed tags, special characters that aren't escaped, and mismatched opening and closing elements. You can check for these yourself in a text editor, or use a free validator tool online to spot the issues before you try converting.
This guide walks you through the steps to prepare your XML file, what to look for, and how to fix the problems you find.
Key Takeaways
- Open your XML file in a plain text editor like Notepad or VS Code, not in Word or Google Docs, which add invisible formatting that breaks XML structure.
- Check that every opening tag has a matching closing tag in the correct order, and that the root element wraps all other content.
- Use a free online XML validator to scan for errors you might miss by eye, such as unescaped special characters or duplicate attribute names.
- Back up your original file before making changes, so you can revert if something goes wrong during editing.
- Test the converted file in the target format to make sure the data came through correctly and nothing was lost or corrupted.
Open the file in a text editor, not a word processor
The first step is to open your XML file in a plain text editor. This means Notepad (Windows), TextEdit (Mac), VS Code, Sublime Text, or Atom — not Microsoft Word, Google Docs, or Apple Pages.
Word processors add hidden formatting codes that break XML structure. When you save a file in Word, it wraps your content in extra markup that makes the file invalid. A text editor saves only the characters you type, which is what XML needs.
If you are on Windows and only have Notepad, that works fine for small files. For larger files or if you want to see line numbers and syntax highlighting (which helps spot errors), read VS Code or Sublime Text — both are free.
Check that all tags are properly closed and nested
XML requires every opening tag to have a matching closing tag. An opening tag looks like <name> and the closing tag looks like </name>. If you open a tag, you must close it before you close any tag that wraps around it.
Look for these specific problems:
- A tag that opens but never closes: <address>123 Main St (missing </address>)
- Tags in the wrong order: <name><first>John</name></first> (closing name before closing first)
- A self-closing tag written wrong: <empty> instead of <empty />
- Missing root element: XML files must have one single element that wraps everything else, usually called <root> or the name of your data type
If your file has hundreds of lines, manually checking every tag is slow and error-prone. Use a validator instead (see the next section).
Use a free XML validator to find errors
An XML validator is a tool that reads your file and reports every error it finds. You paste your XML into the validator, click a button, and it tells you the line number and type of problem.
Common free validators include:
- xmlvalidation.com — paste your XML directly into the text box and click Validate
- codebeautify.org/xmlvalidator — also shows you a tree view of your XML structure so you can see nesting at a glance
- freeformatter.com/xml-validator-xsd — lets you upload a file instead of pasting if your XML is very large
The validator will report errors like "Element 'address' is not closed" or "Attribute 'id' was already specified for element 'person'". Each error includes the line number where the problem starts, so you can jump straight to it in your text editor and fix it.
Run the validator again after you fix each batch of errors. Sometimes fixing one error reveals others that were hidden behind it.
Escape special characters that break XML
Certain characters have special meaning in XML and will break your file if you use them in your data. These are: <, >, &, ", and '.
If your data contains any of these characters, you must replace them with their escape sequences:
| Character | Replace with | Example |
|---|---|---|
| < | < | <price>5 < 10</price> |
| > | > | <note>A > B</note> |
| & | & | <company>Smith & Sons</company> |
| " | " | <title value="He said "hello""> |
| ' | ' | <note>It's done</note> |
The most common mistake is forgetting to escape the ampersand. If your data says "Tom & Jerry", you must write it as "Tom & Jerry" in the XML.
Check the XML declaration and encoding
The first line of an XML file should be the XML declaration, which tells the converter what version of XML you are using and what character encoding the file uses. It looks like this:
<?xml version="1.0" encoding="UTF-8"?>
If your file does not have this line, add it at the very top. UTF-8 is the standard encoding and works with almost all conversion tools and languages.
If your file uses a different encoding (such as ISO-8859-1 or Windows-1252), make sure the declaration says so. If the declaration says UTF-8 but your file actually uses a different encoding, the converter will misread special characters and produce garbage output.
To check your file's actual encoding in VS Code, look at the bottom right corner of the window — it shows the encoding. In other editors, check the Save As dialog to see what encoding options are available.
Remove extra whitespace and comments if needed
XML allows blank lines, indentation, and comments (text between <!-- and -->). These do not break the file, but they can make it larger and slower to convert.
If your XML file is very large (over 10 MB), removing unnecessary whitespace and comments can speed up conversion. Most conversion tools have an option to strip whitespace automatically, so you usually do not need to do this manually.
Comments are useful for documenting your data, so only remove them if the conversion tool is struggling with file size. If you do remove them, keep a backup of the original file with comments intact.
Back up your file and test the conversion
Before you convert, save a copy of your XML file with a different name — for example, data_original.xml — so you have the original if something goes wrong.
After you convert the file to the new format, open the converted file and spot-check the data. Look for:
- Missing or garbled text, especially special characters or non-English languages
- Numbers or dates that changed format unexpectedly
- Blank fields that should have had data
- Duplicate rows or missing rows
If the conversion failed or produced bad output, go back to your XML file and check the validator again. There may be an error the validator missed, or the conversion tool may not support your particular XML structure.
Frequently Asked Questions
What if the validator finds errors but I do not understand what they mean?
Copy the error message into a search engine along with the word "XML" — you will usually find explanations and examples. The most common errors are unclosed tags, duplicate attributes, and unescaped special characters. If you are still stuck, paste a small section of your XML into an online XML formatter, which will highlight the problem visually.
Can I convert an invalid XML file anyway?
Some conversion tools will try, but the output will be incomplete or corrupted. It is faster to fix the XML first using a validator than to debug a broken conversion later. Fixing usually takes minutes; debugging a bad conversion can take hours.
Do I need to understand XML to prepare my file?
No. A validator will tell you exactly what is wrong and where. You just need to follow the error messages and make the changes it suggests. Most preparation is copy-and-paste work, not learning XML syntax.
What if my file is in a different language or uses special characters?
Make sure your XML declaration says encoding="UTF-8" at the top. UTF-8 handles all languages and special characters correctly. If your file uses a different encoding, change the declaration to match what your text editor shows, or re-save the file as UTF-8.
How do I know if my XML is ready to convert?
Run it through a validator one more time. If the validator reports zero errors, your XML is ready. If it reports any errors, fix them and validate again. When validation passes, you can convert with confidence.