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Regex Tester & Parser Playground

Test regular expressions in real time with flags, match index details, and parsed group output.

Matches found: 2

Match List

  • Index: 14

    Match: help@example.com

    Groups: None

  • Index: 34

    Match: admin@codecompileronline.com

    Groups: None

Parsed JSON Output
[
  {
    "index": 14,
    "value": "help@example.com",
    "groups": []
  },
  {
    "index": 34,
    "value": "admin@codecompileronline.com",
    "groups": []
  }
]

How to use regex tester

Enter pattern and flags, then paste text input. Review match index and group details to debug regular expression behavior quickly.

Common regex use cases

Validate email-like strings, extract IDs from logs, parse URLs, and test capture groups before shipping production code.

Common Regex Errors

Invalid regular expression

Check unmatched parentheses, brackets, or escape sequences.

No matches found

Verify flags like g, i, or m and confirm your pattern fits input text.

Unexpected capture groups

Use non-capturing groups (?:...) where you do not need group outputs.

Basic Regex Topics with Examples

Learn character classes, quantifiers, and anchors before writing advanced production patterns.

Character Classes

Character classes let you match groups like digits, words, and whitespace. They are the first step in practical regex building.

\d+        // one or more digits
\w+        // one or more word characters
[a-zA-Z]+  // only letters

Key takeaway: Use character classes to narrow matches before adding complexity.

Quantifiers

Quantifiers define how many times a token appears. They make patterns flexible for varying input lengths.

a*   // zero or more
a+   // one or more
a?   // optional
a{2,4} // between 2 and 4

Key takeaway: Pick strict quantifiers to reduce false-positive matches.

Anchors

Anchors match positions instead of characters. Start and end anchors help validate entire strings.

^hello   // starts with hello
world$   // ends with world
^\d{10}$ // exactly 10 digits

Key takeaway: Use anchors for strong validation patterns like IDs and phone numbers.

Simple Email Pattern

A practical starter pattern can validate common email-like strings for frontend checks.

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

Key takeaway: Keep email regex practical; avoid over-complicated patterns unless required.

Advanced Regex Topics with Examples

Move to grouped extraction, lookaheads, and flag-driven parsing for real-world text processing.

Capturing vs Non-capturing Groups

Capturing groups store matched segments while non-capturing groups help grouping without adding unnecessary captures.

(https?)://(\w+\.\w+)   // capturing groups
(?:https?)://(\w+\.\w+) // first group non-capturing

Key takeaway: Use non-capturing groups when group data is not needed.

Lookaheads

Lookaheads validate future context without consuming characters. Useful for password and token rules.

^(?=.*[A-Z])(?=.*\d).{8,}$
// at least one uppercase, one digit, min length 8

Key takeaway: Lookaheads are strong for multi-rule validation in one pattern.

Global and Multiline Flags

Flags alter regex behavior. g finds all matches, i makes case-insensitive, and m changes line boundary behavior.

/error/gi
/^todo:/gm

Key takeaway: Always verify flags because they change result count and matching positions.

Log Parsing Example

Regex is effective for extracting IDs, levels, and timestamps from logs before analysis or monitoring.

const line = "[ERROR] 2026-02-23 userId=42";
const match = line.match(/\[(\w+)\]\s(\d{4}-\d{2}-\d{2}).*userId=(\d+)/);
console.log(match?.slice(1));

Key takeaway: Use grouped extraction for operational logs and analytics pipelines.

Regular Expression Tester & Debugger

Our regex tester is an online tool for testing, debugging, and learning regular expressions. Write a regex pattern and test text, then instantly see which parts match, view captured groups, and understand how your pattern works. Perfect for developers validating email addresses, phone numbers, URLs, and complex text patterns. See real-time feedback with color-coded matches and detailed information about capture groups.

Why Learn Regular Expressions?

🔍 Pattern Matching

Regular expressions are powerful tools for finding, validating, and manipulating text. Used in almost every programming language for pattern matching and text processing.

✔️ Data Validation

Validate email addresses, phone numbers, URLs, passwords, and custom formats. Regex makes validation easier and more reliable than manual string checking.

📝 Text Processing

Extract data from text, replace patterns, parse structured data, and manipulate strings efficiently. Regex is essential for data extraction and transformation.

💼 Professional Skill

Regular expressions are tested in coding interviews and required for many development roles. Mastering regex makes you a more versatile developer.

Common Regex Patterns to Understand

  • Email Validation - Matches valid email addresses with pattern containing word characters, @ symbol, and domain
  • Phone Numbers - Pattern for XXX-XXX-XXXX format using \d to match digits and hyphens
  • URLs - Matches web addresses starting with http:// or https:// followed by domain and extension
  • Passwords - Requires at least one uppercase letter, one digit, and minimum 8 characters using positive lookahead assertions
  • Hex Colors - Matches 3 or 6 digit hex color codes preceded by # symbol (e.g., #FF5733 or #ABC)
  • Date Format - Matches dates in YYYY-MM-DD format with verification that each part uses correct number of digits

How to Use Our Regex Tester

  1. Enter Your Pattern - Type or paste a regular expression into the pattern field (e.g., `/\d+/` matches numbers)
  2. Enter Test Text - Paste the text you want to test the pattern against in the test string field
  3. View Real-Time Results - Matches appear highlighted in color immediately as you type
  4. Check Capture Groups - See detailed information about captured groups below the results
  5. Adjust Flags - Use flags like `g` (global), `i` (case-insensitive), `m` (multiline) to refine your pattern
  6. Learn and Iterate - Experiment with different patterns to understand how they work

Regex Flags Explained

g (Global) - Find all matches, not just the first one

i (Ignore Case) - Pattern matching is case-insensitive (A and a are treated the same)

m (Multiline) - Treat ^ and $ as line boundaries instead of string boundaries

s (Dotall) - Make . match newline characters as well

Regex Character Classes

  • \d - Any digit (0-9)
  • \D - Any non-digit character
  • \w - Any word character (letters, digits, underscore)
  • \W - Any non-word character
  • \s - Any whitespace character (space, tab, newline)
  • \S - Any non-whitespace character
  • [abc] - Any character in the set (a, b, or c)
  • [^abc] - Any character NOT in the set

Perfect For

  • Developers validating user input in web forms
  • Data processing and text extraction tasks
  • Learning regex fundamentals with instant feedback
  • Debugging regex patterns that aren't working correctly
  • Interview preparation for coding positions
  • Quickly testing patterns before using in production code