Regex Search
Paste text, type a regular expression or literal string, and get back every line that matches — grep-style, with line numbers and surrounding context. Toggle case-insensitive, whole-word, invert, and highlighting. Runs in your browser; nothing is uploaded.
About this tool
Regex Search is a browser-based grep for pasted text. Drop in a log, a config
file, or any block of text, type a regular expression (or a plain literal
string), and get back every whole line that matches — with 1-based line
numbers, an optional window of surrounding context lines, and match
highlighting. It runs entirely in your browser with pure-Rust WebAssembly:
nothing you paste is uploaded anywhere.
It mirrors the flags you already know from Unix grep: ignore case (-i),
whole-word only (-w), invert to show the lines that don't match (-v),
fixed-string/literal mode (-F), context lines (-C), and line numbers (-n).
Worked example
Paste this text:
starting up
ERROR disk full
retrying
ERROR timeout
done
with the pattern ERROR and line numbers on, and you get:
2 matching lines:
2:ERROR disk full
4:ERROR timeout
Each hit line is prefixed with line-number:. Turn on Context lines and the
surrounding lines appear with a line-number- prefix, and non-adjacent groups
are separated by a -- line — exactly like grep -C.
Limits & notes
- Matching uses Rust
regexsyntax. It is fast and linear-time, but it does not support backreferences or look-around assertions (\1,(?=…),(?<=…)); rewrite those patterns without them. - Search is line-oriented:
^and$anchor the start and end of each line, so a pattern never matches across a line break. - Highlighting wraps matches in
«and»markers (the output is plain text, so it stays copy-paste safe); context lines are never highlighted. - To pull out the matched substrings or a capture group instead of whole lines, use the regex-extract tool; to debug a pattern's spans and capture groups, use the regex-tester tool.
FAQ
What is the difference between this and a "find in page" search?
Browser find highlights matches in place; this returns a clean, copy-pasteable
list of just the matching lines, with line numbers and an optional context
window. It also understands full regular expressions, invert, whole-word, and
case-insensitive matching — the way grep does on the command line.
Which regex syntax is supported?
The Rust regex crate syntax: character classes ([a-z], \d, \w, \s),
anchors (^, $, \b), quantifiers (*, +, ?, {2,5}), groups, and
alternation (ERROR|WARN). Backreferences and look-around (\1, (?=…)) are
not supported, which is what keeps matching guaranteed linear-time even on
large inputs.
How do I search for a literal string with special characters?
Turn on Literal. In literal mode every regex metacharacter is escaped, so a
pattern like a.c matches only the exact text a.c and not abc. It's the
equivalent of grep -F.
Can I show a few lines around each match?
Yes — set Context lines to the number of lines you want before and after
each hit (like grep -C N). Context lines are prefixed with - instead of :,
overlapping windows are merged, and separate groups are divided by a -- line.
Is my text uploaded to a server?
No. All matching happens locally in your browser via WebAssembly. The text you paste never leaves your machine.
Developer & Automation Access
Run it from the terminal
Same engine as this page, headless — via the gizza CLI:
gizza tool regex-search "Paste the text or log to search…" 'pattern=e.g. ERROR|WARN'New to the CLI? Get gizza →
Open it by URL
Pre-fill and auto-run this tool with query parameters — the names match the API/CLI:
https://gizza.ai/tools/regex-search/?text=Paste%20the%20text%20or%20log%20to%20search%E2%80%A6&pattern=e.g.%20ERROR%7CWARN&literal=true&ignore_case=true&whole_word=true&invert=true&context=0&line_numbers=true&highlight=trueMachine-readable descriptor: tool.json — title + parameters JSON Schema for agents.