Regex Tester & Debugger

What Is a Regex Tester?

A regex tester lets you write a regular expression pattern and immediately see which parts of your test text it matches — with visual highlighting. Instead of writing regex in code, running the program, and checking output, you see matches update in real time as you type. This tool uses JavaScript's native RegExp engine, the same engine that runs in Node.js and all modern browsers.

How to Use the Regex Tester

1. Enter your pattern. Type your regular expression in the pattern field — without the surrounding slashes. For example, \d3-\d4 matches a phone number fragment.
2. Set your flags. Toggle g for global (find all matches, not just the first), i for case-insensitive, and m for multiline.
3. Paste your test string. Enter the text you want to test against. Matches highlight in real time.
4. Inspect and refine. Review highlighted matches and capture groups. Adjust the pattern until it matches exactly what you need before putting it in production code.

Who Is This For?

• Developers validating input patterns before putting regex in production code — test your email, phone, URL, or date validation pattern against real examples before it ships.
• Data analysts extracting patterns from text — build a regex to extract log entries, parse structured fields from unstructured text, or filter records by pattern.
• Anyone learning regex who needs instant visual feedback — seeing matches highlight in real time as you type is the fastest way to understand what each part of a pattern does.

Key Benefits

• 100% private — your patterns and test strings never leave your browser; no data is transmitted to any server.
• Completely free — no subscription, no sign-up, no paywall.
• No account required — open the page and start testing immediately.
• Real-time match highlighting — matches update as you type, so you can see the effect of each character you add to your pattern without clicking a button.

Common Use Cases

A developer writes an input validation regex for a US phone number format and tests it against 20 sample values to confirm it matches valid numbers and rejects invalid ones. A data engineer builds a regex to extract IP addresses from a server log file and tests it against a sample log block before putting it in a parsing script. A backend developer tests a URL validation pattern to confirm it handles edge cases — trailing slashes, query strings, fragment identifiers — before adding it to form validation.

Common Regex Flags

• g (Global): By default, regex stops after the first match. The global flag continues searching for all matches throughout the entire string.
• i (Case-insensitive): Makes a match both a and A.
• m (Multiline): Changes ^ and $ to match the start and end of each line rather than the entire string.
• s (Dotall): Allows the dot . to match newline characters. By default, a dot matches any character except line breaks.

Regex Cheat Sheet

Frequently Asked Questions