What do the g, i, and m flags mean in regex?

The g (global) flag searches for all matches in the string rather than stopping at the first match. The i (case-insensitive) flag ignores letter casing differences. The m (multi-line) flag forces start (^) and end ($) anchors to match boundary points of lines rather than the entire string.

How do capture groups work?

Capture groups are sections of a regex pattern enclosed in parentheses (e.g., (\d{3})). They allow you to extract sub-matches or structured sections from the overall matched text.

Is my test string data private?

Yes. All regex execution, matching calculations, and highlights are performed entirely in your browser using local JavaScript RegExp APIs. No data is sent over the internet or logged on databases.

What happens if I write an invalid regex pattern?

If the regex pattern is mathematically invalid, the tool catches the JavaScript compilation error and safely prints a clear error message below the input fields without crashing.

Can I copy the compiled regex pattern?

Yes. The tool features a copy shortcut that formats your pattern and active flags into a standard JavaScript RegExp format (e.g. /pattern/gim) and copies it to your clipboard.

🔒 100% Private – nothing uploaded to a server

Regex Tester

Name: Regex Tester
Author: EverTools

Test regular expressions in real-time with live matching, flag configurations, and capture groups.

Quick Answer & Summary

The EverTools Regex Tester validates and processes regular expressions in real-time client-side, showing color-coded match highlights and capture group breakdowns.

Pattern Configurations

Regex Pattern

Active Flags

Regex Compiled SuccessfullyFound 0 matches inside your test string.

Test String

Highlighted Matches

Send requests to support@evertools.org or sales@evertools.org. Invalid email: test@domain, user.name@company.

How to Use Regex Tester

Follow these simple step-by-step instructions to process your files or content.

Enter Regex Pattern

Type your regular expression pattern without the surrounding slashes into the pattern input field.

Configure Toggles

Select flags like Global (g), Case-Insensitive (i), or Multi-line (m) to modify matching behavior.

Provide Test String

Paste or write your test string; matches are highlighted inline instantly as you edit.

What are Regular Expressions and Why do Developers Use Them?

Regular Expressions (often abbreviated as Regex or Regexp) are structured sequences of characters that define specific search patterns. They are used in software development, data parsing, and system administration workflows to evaluate string patterns. By using regex, developers can scan through extensive text files, validate form fields (such as phone numbers, emails, or postal codes), extract sub-elements from configuration blocks, or perform complex search-and-replace transformations in seconds.

Writing regular expressions can be complex due to the compact and symbolic syntax. Forgetting to escape control characters, misconfiguring group bounds, or choosing the wrong matching flags can cause scripts to fail or behave unpredictably. A real-time regex validator helps developers verify and test patterns visually before writing them into code.

Common Regex Search Patterns

Here are some of the most common regular expressions used by web developers:

Email Validation: \b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}\b matches standard email formats (like user@example.com).
US Phone Numbers: \b\d{3}-\d{3}-\d{4}\b matches formats like 555-555-5555.
IP Address (IPv4): \b(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\b validates standard internet protocol addresses.

Step-by-Step: How to Use the Regex Tester

Testing and validating regular expressions is instant and offline:

Input your regex pattern: Enter your expression (without the starting and ending slashes) into the pattern input field.
Set matching flags: Click the flag toggles to select Global (g) for matching all occurrences, Case-Insensitive (i) to ignore capitalization, or Multiline (m).
Provide test text: Paste or write your test string into the textarea. The matches will highlight inline instantly in the output preview.
Review capture groups: Inspect the match list below the editor panes to view index positions and capture group extractions.
Copy output code: Click the copy link next to the pattern input to copy the formatted RegExp string.

Frequently Asked Questions

Everything you need to know about safety, privacy, performance, and usage limits.

A regular expression is a sequence of characters that forms a search pattern. It is used by programmers to perform search, replace, and validation operations on text strings (such as validating email patterns).

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