Regex Tester Pro

Why use this tool?

• A pattern that looks right often matches too much or too little, and the quickest way to find out is to see the hits highlighted in real text.
• Capture groups are hard to reason about in your head; a table showing each match with its $1, $2 and named groups shows what a replace will actually use.
• Nested quantifiers such as (a+)+ can run for minutes on the wrong input. Finding that out in a test tab is better than finding it in production.
• Starting from a working pattern for an email, URL or date is quicker than writing one from memory.

How to use Regex Tester

1. Enter the expression between the slashes in the Pattern field, without the slashes themselves.
2. Toggle the flags you need: global, ignore case, multiline, dot matches newline, unicode or sticky.
3. Paste your sample into Test against. The text below Matches shows every hit highlighted.
4. Check the Match by match table for each match's position and capture groups.
5. To preview a substitution, tick Show what a replacement would do and type the Replace with text, using $1, $<name> or $&.
6. Click Copy matches to put the matched strings on your clipboard, one per line.

Features

• Live results about 200 ms after you stop typing
• Six flags: g, i, m, s, u and y
• Highlighted matches inside the original text
• Per-match table with index, full match and numbered capture groups, and a list of named groups
• Replacement preview with $1, $<name>, $& and $$
• Nine starter patterns: email, URL, IPv4, ISO date, hex colour, slug, HTML tag, duplicate word and named groups
• One-second time limit that stops catastrophic backtracking
• Counts of matches, groups and named groups

Supported formats

Uses the JavaScript (ECMAScript) regular expression engine of your browser, so syntax such as lookbehind and \p{...} follows what that browser supports. Input is plain text; output is highlighted text, a table and, optionally, the replaced text.

Tips

• A pattern that is stopped after a second usually has nested quantifiers like (\w+)* or (a+)+; rewrite it so only one quantifier can claim a given character.
• Turn on the m flag when you use ^ and $ to mean the start and end of each line rather than of the whole text.
• Add the u flag before using \p{L} or other Unicode property escapes.
• The table lists the first 50 matches and the engine reports at most 2,000, so test large inputs in a smaller slice.

Frequently asked questions