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🔍 Regex Tester

Write · Real‑time match · Syntax highlight · Capture groups · String replace

📝 Regular Expression

⚙️ Match Options

g (global) i (ignore case) m (multiline) s (dot matches newline)

📄 Test Text

✅ Valid regular expression

🎯 Match Results

Found 3 matches

🔄 Replace Result

📋 Common Regex Templates — Click to load

📧 Email

\w+@\w+\.\w+

📱 Phone number

1[3-9]\d{9}

🌐 IP address

\d{1,3}\.\d{1,3}\.\d{1,3}\.\d{1,3}

🔗 URL

https?:\/\/[\w\.-]+\.[a-z]{2,}

🔤 Chinese characters

[\u4e00-\u9fa5]+

📅 Date time

\d{4}-\d{2}-\d{2} \d{2}:\d{2}:\d{2}

📚 Regex Quick Reference

Basic characters . any char
\w word char
\d digit
\s whitespace

Quantifiers * 0+
+ 1+
? 0 or 1
{n,m} n to m

Anchors ^ start of line
$ end of line
\b word boundary
(?=) lookahead

Character classes [abc] a/b/c
[^abc] not a/b/c
(a|b) a or b
() capture group

📖 Online Regex Tester: From Debugging to Mastery

Regular expressions are the Swiss Army knife for text processing – used for data validation, text extraction, string replacement, and syntax parsing. ng.cc's online regex tester provides a real‑time environment for writing, matching, and replacing, with support for g/i/m/s flags, match positions, capture groups, and replacement preview. Includes 6 common templates and a quick reference cheat sheet. 100% client‑side, zero data upload.

⚡ Real‑time matching

Type and see matches instantly: match positions, context preview, capture groups. Toggle global/ignore case/multiline flags.

🎯 Capture group analysis

Automatically detect capture groups and display each group's content. Easily debug complex regex.

🔄 String replacement

Supports $& (full match), $1-$9 (capture groups). Live preview, one‑click copy result.

📚 6 common templates

Email, phone, IP, URL, Chinese characters, date/time. One‑click load, get started instantly.

🎯 Regex Use Cases

📋 Form validation: Real‑time check for phone, email, ID, password strength.
🔍 Log analysis: Extract IPs, timestamps, error codes from massive logs.
🔄 Batch replacement: Unify date formats, remove extra spaces in documents.
📊 Data cleaning: Extract plain text from HTML, filter special characters.
💻 Code refactoring: Bulk rename variables, transform API calls.

💡 Regex Pro Tips

🔹 Non‑greedy matching

*? +? ?? {n,m}? By default quantifiers are greedy (match as much as possible). Add ? to make them lazy. Example: <div>.*?</div> matches the shortest div tag.

🔹 Lookahead

(?=pattern) matches a position followed by pattern, without consuming characters. Example: \d+(?=px) matches digits that are followed by "px".

🔹 Lookbehind

(?<=pattern) matches a position preceded by pattern. Example: (?<=\$)\d+ matches digits after a dollar sign.

❓ Frequently Asked Questions

❓ Q1: What's the difference between JavaScript regex and PCRE?

This tool uses the JavaScript RegExp engine. Compared to PCRE (Perl‑compatible), JS lacks \A, \Z, \G, recursive matching, balancing groups, etc. However, for everyday validation, extraction, and replacement, JS regex is more than enough. For testing PCRE patterns, use a dedicated tool.

❓ Q2: Why does my regex sometimes freeze?

Certain complex patterns (e.g., nested quantifiers like (a+)+b) can cause catastrophic backtracking on certain inputs, making the browser hang. This tool includes protection against long runs, but we recommend: 1) avoid nested quantifiers; 2) use non‑greedy quantifiers; 3) break complex regex into steps. If it freezes, just refresh the page.

❓ Q3: How to match Chinese characters?

Use the Unicode range: [\u4e00-\u9fa5] for a single Chinese character, [\u4e00-\u9fa5]+ for multiple. Note: this covers common Han characters but not rare extensions. For full Han support, use \p{Script=Han} (requires u flag).

❓ Q4: Does it support lookarounds?

Yes, fully. Positive lookahead (?=), negative lookahead (?!), positive lookbehind (?<=), negative lookbehind (?<!). Example: \w+(?=@) matches the username part of an email.

❓ Q5: Is my data sent to any server?

Absolutely not. This is a static HTML page – all regex matching and replacement happens inside your browser's JavaScript engine. You can even go offline and it still works. Your test text and patterns never leave your device, making it safe for sensitive data.

❓ Q6: How can I export the results?

You can copy the content from the "Match Results" area, or use the "Replace Result" function to transform matches and copy the output. File export is not currently supported; we suggest pasting the results into your local editor.

🔗 Recommended Tools

This regex tester is part of the ng.cc text‑processing toolkit. You might also like:

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⚡ All processing happens locally – your regex and data never leave your browser.

⚡ 100% client‑side · Zero network requests · Quick reference included

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