Regex Tester

It runs a JavaScript regular expression against your test text and shows you exactly what matched: highlighted in context, and listed with each match's position and capture groups. Everything updates as you type, so you can build a pattern incrementally rather than guessing.

1. Type your pattern into the field between the slashes — no delimiters needed.
2. Tick the flags you want; the full literal is shown beneath them.
3. Paste your test text below, then watch the matches highlight as you type.
4. Read the table for each match's position and captured groups.

• g — find every match rather than stopping at the first.
• i — case-insensitive matching.
• m — ^ and $ match at each line break, not just at the start and end of the whole string.
• s — . also matches newline characters, which it does not by default.
• u — full Unicode mode, needed for \p{...} property escapes and correct handling of characters outside the basic plane.

Anything in parentheses is captured and listed alongside its match. Named groups — (?<year>\d{4}) — appear by name, which makes a long pattern far easier to read later. Use (?:...) for a group you want to apply a quantifier to but do not need to capture.

A group that takes part in no match shows as (no match) rather than being silently omitted.

• Building a validation pattern and checking it against genuine edge cases.
• Extracting fields from log lines or a text export.
• Working out why a pattern that looks right is matching nothing.
• Testing a search-and-replace before running it across a codebase.

• This uses the JavaScript regex engine. PCRE, Python, Go (RE2) and Java differ in real ways — lookbehind support, atomic groups, recursion, named-group syntax. A pattern that works here may not work identically elsewhere.
• Results are capped at 1,000 matches, and the detail table shows the first 200, to keep the page responsive.
• A catastrophically backtracking pattern such as (a+)+$ against a long non-matching string can lock the tab. This is inherent to backtracking engines, not to this page — and it is exactly why such patterns are a denial-of-service risk in production.
• Zero-length matches are marked in the highlighted view but have no width, since there is nothing to highlight.
• Your pattern is compiled as a regular expression, never evaluated as code. No JavaScript you type here is executed.