How to Test Regular Expressions Online

Regular expressions (regex) are one of the most powerful tools in a developer's arsenal — and one of the most intimidating. A well-crafted regex can validate emails, parse logs, extract data, and transform text in a single line. But getting regex patterns right often requires trial and error.

That's where an online regex tester comes in. In this guide, we'll cover regex basics, common patterns, and how to test your regular expressions instantly using ToolMix's free Regex Tester.

What Are Regular Expressions?

A regular expression is a sequence of characters that defines a search pattern. Regex is used across virtually all programming languages for string matching, validation, search-and-replace, and data extraction.

For example, the pattern \d{3}-\d{3}-\d{4} matches US phone numbers like 555-123-4567.

Essential Regex Syntax

• •. (dot) — Matches any single character except newline
• •\d — Matches any digit (0-9)
• •\w — Matches any word character (letters, digits, underscore)
• •\s — Matches any whitespace character
• •* — Matches 0 or more of the preceding element
• •+ — Matches 1 or more of the preceding element
• •? — Matches 0 or 1 of the preceding element
• •{n,m} — Matches between n and m occurrences
• •[abc] — Matches any character in the set
• •(group) — Captures a group for extraction
• •^ — Matches the start of a string
• •$ — Matches the end of a string

How to Test Regex Online (Step-by-Step)

Step 1: Open the Regex Tester

Go to ToolMix's free Regex Tester. It uses JavaScript regex syntax and provides real-time match highlighting as you type.

Step 2: Enter Your Pattern

Type your regular expression pattern in the regex input field. Don't include the surrounding slashes — just the pattern itself.

Step 3: Set Flags

Toggle the flags you need: g (global — match all occurrences), i (case-insensitive), m (multiline), s (dotAll — dot matches newline).

Step 4: Enter Test Text

Paste or type the text you want to test against. Matches will be highlighted in real-time as you adjust the pattern and text.

Common Regex Patterns

• •Email: ^[\w.-]+@[\w.-]+\.[a-zA-Z]{2,}$
• •URL: https?://[\w.-]+(?:/[\w.-]*)*
• •Phone (US): \(?\d{3}\)?[-. ]?\d{3}[-. ]?\d{4}
• •IP Address: \b\d{1,3}(\.\d{1,3}){3}\b
• •Date (YYYY-MM-DD): \d{4}-(?:0[1-9]|1[0-2])-(?:0[1-9]|[12]\d|3[01])
• •Hex Color: #(?:[0-9a-fA-F]{3}){1,2}

Frequently Asked Questions