Filter a log file
Like the grep command, but in the browser: the log stays on your computer, the matches update as you type, and a pattern with capture groups turns into a table you can open in a spreadsheet.
- Runs entirely in your browser
- Works offline
- No upload
- No sign-up
- No watermark
Loading the tool…
How it works
- Drop the log file, or paste lines.
- Type a filter: plain text, or a regular expression with capture groups (parts in parentheses).
- Download the matching lines, or the captured parts as a CSV table.
Why nothing is uploaded
Every operation on this page is done by code running inside your browser tab, using the same engine that renders web pages. The file is read from disk into your tab’s memory, transformed there, and written back out as a download. It is never sent anywhere — not to us, not to a third party.
Verify it yourself
- Open your browser’s developer tools (F12) and select the Network tab.
- Load your file and run the tool.
- The only requests you will see fetch the tool’s own code — and, for a few heavy tools, their open-source engine from a public CDN — plus one small page-view ping to loreatec.jp (page address and title, nothing more). None of them carry your file.
Frequently asked questions
How big a file can it handle?
Tens of megabytes are fine: the file is split into lines in memory and filtered on every keystroke. For a gigabyte of logs, use the grep command on your computer instead — a browser tab is the wrong tool for that.
What do capture groups do here?
They turn extraction into columns. A pattern such as "GET (\S+) (\d{3})" on a web server log gives you a table of paths and status codes, downloadable as CSV. It is the step between “find the lines” and “analyse them in a spreadsheet”.
Does it read Shift-JIS logs?
Yes. The character encoding is detected before the file is split into lines, so logs from older Japanese systems show up readable instead of as garbled characters (mojibake).
What is “Invert” for?
Because the second thing everyone does with a log is remove the noise: hide the health checks, the static files, the DEBUG lines, and look at what is left. Invert shows the lines that do NOT match — the same as grep -v.