What is a log file?
A log file records events one per line: a timestamp, a level or status, and a message. Each tool has its own layout, from plain text to JSON lines, the Apache combined format and syslog.
Log parsers break on multi-line stack traces, timestamps out of order, ANSI colour codes, very long lines and CRLF endings. The generator adds each on request so you can test ingestion, search and alerting.
Anatomy of a log file
timestampISO 8601 in UTC, or the format's own stylelevelDEBUG, INFO, WARN, ERROR or FATALlogger / appWhere the event came frommessageFree text, sometimes with key=value pairsstack traceExtra lines after an error (plain text)<PRI>Syslog priority: facility × 8 + severity
What you can generate
- Seven layouts: plain, JSON lines, logfmt, Apache/Nginx combined, Nginx error, syslog RFC 5424 and RFC 3164
- Java, Python or Node.js stack traces on errors
- Out-of-order timestamps and blank lines
- Unicode, ANSI colour codes and 10 KB lines
- CRLF line endings
- Addresses from the documentation ranges, hosts on example.test
How to make one
- Open the log generator, or start from a preset above.
- Set the size and switch on the edge cases you need; the preview and size estimate follow every change.
- Generate, then download. The file is made in your browser, and the same preset and seed always give you the same file.
Questions
No. Addresses come from the ranges reserved for documentation (192.0.2.0/24, 198.51.100.0/24, 203.0.113.0/24) and hosts are on example.test.
RFC 5424 (with structured data and an optional UTF-8 BOM before the message) and the older BSD format from RFC 3164.
As an error object with the type, message and the whole trace in one string, so each event stays on one line.