Free LOG test files and sample generator
Timestamped, level-tagged log lines. Generate valid .log sample files for testing log viewers, parsers, monitoring and grep pipelines.
What is a .log file?
LOG: Application Log File. Log files are append-only text with one timestamped event per line. They are the input to every monitoring and observability tool, and they grow without bound, which is what makes size behavior worth testing.
Why generate a test LOG file?
- Test a log parser, shipper or tailing UI against a large file.
- Check rotation, truncation and disk-limit handling.
- Exercise a regex or Grok pattern against consistently formatted lines.
How a .log file is identified
A .log 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
Rows and lines are generated to fill the target, and the last line is padded to land on the exact byte.
Negative testing with broken LOG 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 LOG content
2026-07-28 12:00:00 INFO event 0 value=137 2026-07-28 12:01:00 INFO event 1 value=274
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
Any text editor or `tail -f`; parse with `grep`, `awk`, or a log-shipping agent.
Media type text/plain · extension .log · category Data
Generate a .log file → · questions about sizes, privacy or cost are answered on the site FAQ.
Frequently asked questions about LOG files
What identifies a .log 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 .log file be an exact number of bytes?
Rows and lines are generated to fill the target, and the last line is padded to land on the exact byte.
Can I download several broken LOG files at once?
Yes, select more than one File Condition and you get one ZIP containing a .log per condition, each named after its condition.
Can the LOG file use UTF-16 or a byte-order mark?
Yes. .log 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 LOG file?
Any text editor or tail -f; parse with grep, awk, or a log-shipping agent.