Regex Tester
Test regular expressions against sample text. See all matches highlighted, with group captures listed below.
About the Regex Tester
A regular expression, or regex, is a compact pattern for finding and matching text. Developers use them to validate input such as email addresses, to search and replace across files and to extract pieces of text from logs. A tester lets you try a pattern against sample text and see matches highlighted straight away.
The building blocks are a small set of symbols. A dot matches any character, a star means zero or more, a plus means one or more and a question mark means optional. Square brackets define a set, so [a-z] matches any lower case letter, and parentheses create groups you can capture. Anchors ^ and $ match the start and end of a line. Flags change behaviour: g finds all matches and i ignores case.
Two things catch people out. Quantifiers are greedy by default and match as much as possible, so use a lazy form such as .*? for the shortest match. And badly written patterns with nested repetition can cause catastrophic backtracking, where the engine takes a very long time on certain inputs.
The pattern \d{4}-\d{2}-\d{2} matches dates in the form 2026-10-01. Wrapping each part in parentheses lets you capture the year, month and day separately.
Tips for best results
- Build the pattern in small steps and test after each addition.
- Escape special characters with a backslash to match them literally, such as \. for a dot.
How to use the Regex Tester
Why use Toolseza for Regex Tester?
Use this tool as often as you need with no paywalls, premium tiers, or hidden daily calculation quotas.
All calculations and file manipulations run inside your web browser. Your inputs are never sent to a cloud server.
Results update in real-time as you type or adjust settings, with instant one-click copy and export capabilities.
Works natively on smartphones, tablets, laptops, and desktop computers with zero installation or account creation.
Editorial Standards & Verification: All formulas, algorithms, and conversion factors implemented on Toolseza adhere to openly documented international standards (ISO, NIST, BIPM, W3C). Results are verified against benchmark reference datasets before publication.
Frequently Asked Questions
Is Regex Tester free to use?
Yes — Regex Tester is completely free, unlimited, and requires no sign-up.
What regex flavour does this tester use?
The tester uses JavaScript's native RegExp engine, which follows the ECMAScript regex standard. Common features like lookaheads, named groups and character classes are all supported.
Does the output follow the standard spec?
Yes — output follows the standard format, so it's compatible with other tools and libraries.
Does it work on mobile and tablet?
Yes — Regex Tester works on any modern browser, including mobile and tablet, no app required.