Line Filter

Keep or remove lines by keyword or regular expression, without uploading anything. Everything runs locally in your browser.

Features

Keyword or regex — plain keywords are matched literally, so a.c never matches abc. Switch to regex mode for patterns like ^ERROR\b.
Any or all patterns — one pattern per line. Keep lines matching at least one of them, or only lines matching all of them.
Keep or remove — invert the match to delete the matching lines instead of keeping them, like grep -v.
Ignore case — Error and error are the same token unless you turn case sensitivity on.
Drop empty lines — remove blank lines in the same pass.
Counts — see the total number of lines, how many stayed, how many were removed, and how many patterns are active.
Highlighted matches — every matched span in the result is highlighted, so you can see why each line stayed. In remove mode the surviving lines are the non-matches, so nothing is highlighted.
Export — copy the filtered text, move it into the input to keep working on it, or download it as a .txt file.

An invalid regular expression is reported instead of silently dropping every line, so a typo never wipes your output.

All processing stays on your device; no data leaves the browser.