Regex Tester — Test Regular Expressions Online

What is a Regex Tester?

A regex tester provides an interactive environment where you enter a regular expression pattern and a test string, and it highlights all matches in real time. It shows captured groups, match positions, and whether the pattern compiles without errors.

Why Use a Regex Tester?

Regex syntax is dense and error-prone. A small typo creates a pattern that matches nothing — or worse, matches everything. Real-time visual feedback shows exactly what your pattern captures, catches syntax errors immediately, and lets you iterate without rerunning code.

Two Tabs: Tester and Generator

The Tester tab is the classic experience: enter a pattern, set flags, paste text, and matches light up instantly. The Generator tab lets you describe what you want in plain English — like 'email address' or 'ISO date' — and the tool returns a ready-to-use regex pattern with a plain-language explanation of each part.

Key Benefits

• Live match highlighting as you type
• Shows all captures and groups
• Supports flags: g, i, m, s
• Syntax error messages shown immediately
• Generator tab: describe the pattern, get the regex
• Transfer generated regex directly to the Tester tab

How to Use Regex Tester

1. Switch to the Tester tab to test an existing pattern
2. Enter your regex pattern (without slashes) and set flags
3. Paste test text — matches highlight in real time
4. Or switch to the Generator tab
5. Type a plain-English description of the pattern you need
6. Click 'Use in Tester' to transfer the generated pattern for further testing

Example Use Case

Writing a validation regex for email addresses. Switch to Generator, type 'email address', copy the generated pattern, then switch to Tester and paste a list of test emails (valid and invalid). The highlighter shows which ones match — adjust the pattern until only valid emails highlight.

Tips

• Use ^ and $ anchors to match full string, not just a substring
• The g flag finds all matches, not just the first
• Use (?:...) for non-capturing groups
• Escape special characters like . * + ? with backslash
• Use the Generator for common patterns (UUID, ISO date, phone, email) instead of writing from scratch