Free YAML test files and sample generator
Human-friendly data serialization with indentation-based structure. Ubiquitous for config files, CI pipelines and infrastructure definitions.
What is a .yaml file?
YAML: YAML Ain't Markup Language. YAML is the configuration format of modern infrastructure, Kubernetes, CI pipelines, Docker Compose, Ansible. Its indentation sensitivity means small structural mistakes produce a different document entirely, which is precisely what makes bad YAML worth testing against.
Why generate a test YAML file?
- Test a config loader with a large, deeply nested document.
- Confirm your tooling reports a clear error on invalid indentation instead of silently misreading it.
- Validate schema checks in a CI step without committing a real config.
What you can put inside a .yaml file
You get 5 content options for YAML, so the file holds something meaningful rather than random padding: Key–value object, Array of records, Nested structure, Numeric dataset, Mixed data types. Pick several and they are merged into one file, with a section, sheet, slide or folder for each.
How a .yaml file is identified
A .yaml 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 YAML 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 YAML content
id: 1 name: Test User active: true roles: - admin - editor
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
Validate with `yamllint file.yaml` or `python -c "import yaml,sys;yaml.safe_load(open(sys.argv[1]))" file.yaml`.
Media type text/yaml · extension .yaml · category Data
Generate a .yaml file → · questions about sizes, privacy or cost are answered on the site FAQ.
Frequently asked questions about YAML files
What identifies a .yaml 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 .yaml 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 YAML file?
There are 5 content options for .yaml: Key–value object, Array of records, Nested structure, Numeric dataset, Mixed data types. Choose more than one and they are combined into a single file, a section, sheet, slide or folder per option, rather than downloaded separately.
Can I download several broken YAML files at once?
Yes, select more than one File Condition and you get one ZIP containing a .yaml per condition, each named after its condition.
Can the YAML file use UTF-16 or a byte-order mark?
Yes. .yaml 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 YAML file?
Validate with yamllint file.yaml or python -c "import yaml,sys;yaml.safe_load(open(sys.argv[1]))" file.yaml.