Regex Tester

What Is Regex Tester?

Regex Tester is a free online tool that lets you build, test, and debug regular expressions right in your browser. Whether you’re validating an email, extracting IP addresses, or parsing dates, this tool gives you instant feedback as you type. No installation, no setup — just open the page and start matching patterns against sample text.

Designed for developers, data analysts, and anyone who works with text, the regex tester supports common programming languages like Python, Go, Java, PHP, JavaScript, and Ruby. It also includes ready-to-use patterns for Chinese characters, URLs, phone numbers, and more. You can tweak flags (case-insensitive, multiline, etc.) and view match details in real time, making it easy to learn regex or troubleshoot a tricky expression.

Key Features

• Live matching: See highlighted matches, groups, and captures update as you type your regex and test string.
• Built-in pattern library: Quickly insert common regex patterns for emails, IPs, dates, Chinese text, social security numbers, and hexadecimal colors.
• Multi-language code snippets: After building your regex, instantly copy ready-to-use code blocks for Python, Go, Java, PHP, JavaScript, and Ruby.
• Global & multiline flags: Toggle case sensitivity, multiline anchors (^/$), dot-all mode, and Unicode support with one click.
• Group & replacement testing: Enter a replacement string to see substitution results, or inspect captured groups in a structured table.
• Persistent URL sharing: Save your current regex and test input as a shareable link, perfect for debugging with teammates.

How to Test and Generate Regex Online

1. Open the Regex Tester tool at ToolFK and locate the input area labeled “Regular Expression”.
2. Type or paste your regex pattern (e.g., \b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b for email matching) into the first field.
3. In the second field labeled “Test String”, enter the text you want to search through. You can also paste a data sample directly.
4. Adjust the flags (e.g., i for case‑insensitive, m for multiline) by clicking the toggle buttons below the regex field.
5. Watch the matches highlight instantly. Click on any match to see its captured groups in the result panel.
6. Once satisfied, click the “Copy Code” button next to your preferred language (Python, Go, Java, etc.) to get a fully functional snippet that includes the pattern and flags.

Best Use Cases

• Form input validation: Quickly test email, phone, or URL patterns before shipping them into production code.
• Data cleaning and extraction: Extract IP addresses, dates, or Chinese characters from logs or large text files.
• Code review & debugging: Share a persistent regex URL with a colleague to verify a tricky pattern without sending files.
• Learning regex: Experiment with common patterns and see how capture groups, quantifiers, and alternation behave in real time.
• Multi-language prototyping: Write a regex once and copy it as code in Python, JavaScript, Java, PHP, Go, or Ruby — saving minutes of manual conversion.

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Frequently Asked Questions

How do I match an email address using this regex tester?

Use the built‑in email pattern from the library, or type \b[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Z|a-z]{2,}\b. The tool highlights all matches instantly. You can then copy the code snippet for your backend language. If you need to exclude certain domains, simply modify the pattern and watch the results update.

Can I test regex for Chinese characters with this online tool?

Yes. The pattern library includes a preset for Chinese characters ([\u4e00-\u9fff] or \p{Han} with Unicode flag). Paste Chinese text into the test string area. The tool supports Unicode-aware matching when you enable the Unicode flag (u). This is especially useful for validating names or extracting specific characters from mixed-language data.

Why do my matches disappear when I enable multiline mode?

Multiline mode (flag m) changes how ^ and $ behave — they now match the start and end of each line, not the whole string. If your pattern relies on start/end anchors, enable multiline to match each line separately. Otherwise, leave it off. The tool’s live preview lets you toggle the flag and immediately see the effect.

How do I generate a regex for an IP address?

Use the IP address pattern from the library: \b(?:(?:25[0-5]|2[0-4]\d|[01]?\d\d?)\.){3}(?:25[0-5]|2[0-4]\d|[01]?\d\d?)\b. Paste it into the regex field and add a test string containing valid and invalid IPs. The tool will highlight valid ones. You can then copy the pattern as a Python or Java snippet for server‑side validation.

Can I share my regex testing session with others?

Absolutely. After typing your regex and test string, the URL in your browser’s address bar updates automatically with your input encoded. Copy that URL and send it to anyone. When they open the link on ToolFK’s Regex Tester, your exact pattern, flags, and test string will be loaded — no extra steps needed.

Does this tool support lookahead/lookbehind and backreferences?

Yes. The regex engine used in ToolFK’s online tester supports most modern regex features, including positive/negative lookahead ((?=...), (?!...)), lookbehind ((?<=...), (?<!...)), named groups ((?<name>...)), and backreferences (\1, \k<name>). The live highlighting and group table will show you exactly what each part captures.

Last updated: July 1, 2026