What is the LOG file format?
.log is a plain-text file used to store various process logs. A .log file can be generated by an operating system or application - almost any software that runs a persistent process writes one. Because the content is nearly always plain text encoded in UTF-8 or ASCII, it can be opened in any text editor. Each line typically begins with a timestamp (e.g. 2026-06-11 10:42:01) followed by a severity level and a message. What information is written to log files is a design choice made by the developer or administrator. A special instance of the .log file is the error log, which stores only information about process errors.
What do log files contain
Entries in .log files are divided into three categories:
- Error - the process or part of the process encountered an event that prevented it from executing its routines
- Warning - the process or part of the process encountered a problem, but it did not prevent it from executing its routines
- Information - some information pertaining to the execution of a given process
Many modern applications also write Debug and Trace entries during development or active troubleshooting.
Log files can store information such as the history of changes, users logged into the system, or resource access history. Logs can be exported to other file formats - for example .CSV - for further processing and the generation of statistics and reports. Long-running services commonly rotate their logs, renaming the current file to .log.1 and starting a fresh .log. A minority of applications (certain databases, games, or Windows ETL traces) write proprietary binary .log files that can only be opened in their own viewer or a dedicated log-analysis tool.
Security & safety
RISK: LOWA plain-text .log can't execute and is safe to open in a text editor. Two real cautions: (1) logs frequently contain sensitive data - usernames, IP addresses, file paths, tokens, even passwords - so scrub them before posting publicly or attaching to a forum; (2) never trust a .log that has an unusually large size and asks to be 'run', and be wary of files that pretend to be logs but have a double extension (report.log.exe). Deleting old rotated logs is generally safe; an active log may be locked by the running program.
Format details
in a nutshell- Binary/proprietary application logs - A few programs (some games, DB engines, telemetry) write .log in a binary format readable only by their own tooling, not a text editor.
Programs that open LOG files
Windows3 apps
Windows Notepad
Built-in Right-click the .log > Open with > Notepad. Fine for small logs; use Notepad++ for large ones. 
Notepad
Open-source Open the .log; handles big files, syntax highlighting, and has a search to jump to 'error'. Best free choice. 
Visual Studio Code
Free Open the log; great search/filter and a Log file syntax mode. Good for multi-megabyte logs. 
macOS2 apps
Console (Apple)
Built-in For system logs: open Console.app to browse macOS's live and stored system logs (not for arbitrary app .log files). 
Linux1 app
gedit / nano / less
Open-source Open in gedit, or in a terminal use less app.log (and G to jump to the end, /error to search). Technical details
deep spec| Format type | Plain-text, line-oriented event log |
| Typical encoding | UTF-8 or ASCII; older Windows logs may use ANSI (Windows-1252) |
| MIME type | text/plain |
| File signature | None - no magic bytes or fixed header; identified by the .log extension and content heuristics |
| Line structure | One event record per line; each line is self-contained and human-readable |
| Common severity levels | TRACE, DEBUG, INFO, WARN, ERROR, FATAL (in ascending severity order) |
| Timestamp formats | ISO 8601 (YYYY-MM-DD HH:MM:SS), Unix epoch (integer seconds), syslog format (RFC 3164 / RFC 5424) |
| Established log formats | syslog (RFC 5424), Apache/NGINX Combined Log Format, W3C Extended Log Format, JSON-per-line (NDJSON) |
| Newline convention | LF (\n) on Unix/Linux/macOS; CRLF (\r\n) on Windows; most parsers accept both |
| Log rotation | Services rotate by date or size, producing .log.1, .log.2 … or date-stamped copies; logrotate is the standard utility on Linux |
| Binary variant | Some databases, games, and Windows ETL traces write proprietary binary .log files readable only in a dedicated viewer |
| Structured log variants | JSON-per-line, key=value pairs (logfmt), and XML increasingly appear inside .log files for machine parsing |
| Common system locations (Linux/macOS) | /var/log/ and application-specific subdirectories |
| Common system locations (Windows) | %SystemRoot%\Logs\, %APPDATA%\, and %TEMP%\ |
| Released | Convention as old as software logging itself |
| Open standard | Yes · royalty-free |
LOG conversions
Community Q&A
asked by usersNo questions yet - be the first to ask about LOG files.
Frequently asked questions
How do I open a LOG file?
less on Linux. VS Code or Notepad++ are best for large logs.What program opens a LOG file?
Can I delete LOG files?
Why is my LOG file unreadable / full of strange characters?
How do I open a huge LOG file that freezes Notepad?
less bigfile.log opens instantly and lets you search with /.
