Free CSS test files and sample generator
Stylesheet language for the web. Create valid .css files to test parsers, minifiers, editors and asset pipelines.
What is a .css file?
CSS: Cascading Style Sheets. CSS source is plain text, so the interesting part for testing is not the bytes but the size and the surroundings: how your tooling handles a file of this type at a given size, with a given encoding, or when it is truncated mid-token.
Why generate a test CSS file?
- Check that an upload form, code viewer or diff tool accepts a .css file and renders it correctly.
- Exercise size limits in CI artifacts, linters and static-analysis steps without waiting on a real repository.
- Feed a truncated or corrupted copy to a parser to confirm it fails cleanly instead of hanging.
What you can put inside a .css file
You get 3 content options for CSS, so the file holds something meaningful rather than random padding: Definitions, Simple statements, With comments. For CSS these are alternatives, so choose the one that matches what you need to test.
How a .css file is identified
A .css file has no signature at the start. A text format has no identifying leading bytes, so the extension and the reported media type are the only claims about it until a parser actually reads it, which is why validating uploads by extension alone is unsafe.
How the size lands on the exact byte
The format allows comments, so the padding is comment lines, legal, inert, and visible if you open the file.
Negative testing with broken CSS files
- Invalid. Identifiable, but wrong inside, so it fails during parsing.
- Corrupted. The leading bytes are destroyed. Same length as the valid file.
- Incomplete. Truncated part-way, so it is genuinely shorter.
- Empty. Chosen under Content rather than File Condition: valid structure, no data.
Which failure to reach for, and what to assert for each, is covered in how to make a corrupted file for testing. For upload limits and type checks see testing file upload validation, and for this format's encodings, UTF-16 and BOM test files.
Sample CSS content
.cls-1 { color: #0e7490; margin: 1px; }
.cls-2 { color: #0e7490; margin: 2px; }This shows the shape of the file. Your download is generated fresh at the size you choose, so the values will differ.
How to open and verify the file
Open in any editor or browser devtools; lint with stylelint.
Media type text/css · extension .css · category Code
Generate a .css file → · questions about sizes, privacy or cost are answered on the site FAQ.
Frequently asked questions about CSS files
What identifies a .css file?
Nothing at the start of the file does. A text format has no identifying leading bytes, so the extension and the reported media type are the only claims about it until a parser actually reads it, which is why validating uploads by extension alone is unsafe.
How can a .css file be an exact number of bytes?
The format allows comments, so the padding is comment lines, legal, inert, and visible if you open the file.
What can go inside the CSS file?
There are 3 content options for .css: Definitions, Simple statements, With comments. For CSS these are alternatives, so pick the one matching what you need to test.
Can I download several broken CSS files at once?
Yes, select more than one File Condition and you get one ZIP containing a .css per condition, each named after its condition.
Can the CSS file use UTF-16 or a byte-order mark?
Yes. .css is a text format, so it can be generated as UTF-8, UTF-8 with a byte-order mark, UTF-16 LE or UTF-16 BE. The body is shortened before re-encoding so the finished file still lands on the exact size you asked for. Note that a UTF-16 file always has an even byte count.
How do I open or verify the CSS file?
Open in any editor or browser devtools; lint with stylelint.