Regex Tester

Q: What do the flags mean?

g (global) — finds all matches in the string instead of stopping after the first. i (case insensitive) — makes the match case-insensitive, so Hello matches hello, HELLO, etc. m (multiline) — changes ^ and $ to match the start/end of each line rather than the whole string. s (dot all) — makes the . character match newline characters (\n) as well.

Q: What regex flavor is used?

This tool uses JavaScript's built-in RegExp engine, which follows the ECMAScript standard. It supports most modern regex features including lookaheads, lookbehinds (ES2018+), named capture groups, and Unicode mode. It does not support PCRE-specific syntax like (?P<name>...) — use the standard JS syntax (?<name>...) instead.

Test regular expressions with live highlighting — JavaScript RegExp, 100% client-side

Flags: g i m s

Test String

Match Results 0 matches found

Enter a pattern and test string above, then click Test Pattern...

#	Match	Index	Groups
No matches yet — run a test to see results

About Regex Tester

Regex Tester is a free, browser-based utility built for developers and engineers who need a fast, reliable way to test regular expressions with live highlighting — javascript regexp, 100% client-side. Whether you're debugging an API response, preparing data for deployment, or validating configuration files, this tool handles the job in seconds — with zero server calls. Everything runs locally in your browser, so your source code and data stay private.

How to Use

Enter your pattern Type your regular expression in the pattern input field. Do not include surrounding slashes.

Set flags Toggle flags: g (find all matches), i (case insensitive), m (multiline), s (dot matches newline).

Paste your test string Type or paste the text you want to test the pattern against into the Test String area.

See results instantly The tool auto-tests as you type (with a short debounce) or click Test Pattern. Matches are highlighted in yellow and listed in the table with their index and capture groups.

🔒 Privacy note: All regex processing runs in your browser using the built-in JavaScript RegExp engine. Nothing is sent to any server.

Frequently Asked Questions

A regular expression (regex) is a sequence of characters that defines a search pattern. It is used to match, find, and manipulate text. For example, the pattern \d+ matches one or more digits. Regex is supported in virtually every programming language and is an essential tool for text processing.

g (global) — finds all matches in the string instead of stopping after the first.
i (case insensitive) — makes the match case-insensitive, so Hello matches hello, HELLO, etc.
m (multiline) — changes ^ and $ to match the start/end of each line rather than the whole string.
s (dot all) — makes the . character match newline characters (\n) as well.

Check these common issues: (1) Verify your pattern syntax is correct — the status bar shows any errors. (2) Make sure the g flag is enabled if you expect multiple matches. (3) If you are matching case-sensitively, enable the i flag. (4) Ensure you have entered text in both the pattern field and the test string area.

This tool uses JavaScript's built-in RegExp engine, which follows the ECMAScript standard. It supports most modern regex features including lookaheads, lookbehinds (ES2018+), named capture groups, and Unicode mode. It does not support PCRE-specific syntax like (?P<name>...) — use the standard JS syntax (?<name>...) instead.