Regex Tester

What is the Regex Tester?

A regular expression (regex) is a compact pattern language for matching text. Developers use regexes to validate input, extract values from logs, search and replace in editors, and route URLs. They are powerful but easy to get subtly wrong, which is why testing a pattern against real samples before putting it in code is worth the minute it takes.

This tester uses the JavaScript regular expression engine, so behaviour matches what you will get in the browser and in Node.js. Flags change how a pattern works: g finds all matches, i ignores case, m makes ^ and $ match at line boundaries, s lets . match newlines, and u enables full Unicode matching.

When to use the Regex Tester

Build and verify patterns here before they reach your codebase: validating form fields, extracting IDs or dates from logs, rewriting URLs, cleaning data with search and replace, or splitting text by a complex delimiter. Testing against several realistic samples, including inputs that should not match, catches the bugs that otherwise show up in production. It is also a good place to learn, because the instant highlighting makes the effect of each quantifier, anchor and group visible while you experiment.

How to use the Regex Tester

1. Enter your pattern between the slashes, without the surrounding / characters.
2. Toggle the flags you need, such as g and i.
3. Paste sample text into the test area.
4. Matches are highlighted live; the list below shows each match, its index and capture groups.
5. Refine the pattern until only the intended text matches, then copy it into your code.

Examples

Pattern:  (\d{4})-(\d{2})-(\d{2})
Flags:    g
Text:     Released 2026-10-02, patched 2026-10-15.

Match 1:  2026-10-02   groups: 2026, 10, 02
Match 2:  2026-10-15   groups: 2026, 10, 15

Named groups:  (?<year>\d{4})-(?<month>\d{2})
Email (simple):  [^\s@]+@[^\s@]+\.[^\s@]+

Common errors and tips

• Greedy vs lazy: .* grabs as much as possible; use .*? to stop at the first possible end.
• Escape special characters like . ? + * ( ) [ ] { } | \ ^ $ when you want them literally.
• Catastrophic backtracking from nested quantifiers such as (a+)+ can freeze a page; keep patterns simple.
• A pattern with the g flag keeps state in lastIndex when used with .test() repeatedly, a frequent source of confusing bugs.
• Do not validate email addresses or HTML with a regex alone; use a proper parser or confirmation email.

Privacy: runs entirely in your browser

Patterns and sample text, which may include log lines or customer data, are evaluated locally in your browser and never uploaded. This tool runs entirely in your browser: nothing you enter is uploaded, stored or logged on our servers, and it keeps working even if you go offline after the page has loaded.