Regular Expressions (Regex) Cheat Sheet & Online Tester

What are Regular Expressions?

Regular expressions (regex or regexp) are patterns used to match character combinations in strings. They are supported by virtually every programming language and are indispensable for tasks like form validation, data extraction, search-and-replace, and log parsing.

Basic Syntax

• . — matches any single character (except newline)
• ^ — start of string
• $ — end of string
• \d — any digit (0–9)
• \w — any word character (a–z, A–Z, 0–9, _)
• \s — any whitespace character
• \D, \W, \S — negated versions of the above

Quantifiers

• * — 0 or more times
• + — 1 or more times
• ? — 0 or 1 time (optional)
• {n} — exactly n times
• {n,} — n or more times
• {n,m} — between n and m times

Character Classes

• [abc] — matches a, b, or c
• [^abc] — matches anything except a, b, or c
• [a-z] — matches any lowercase letter
• [0-9] — matches any digit (same as \d)

Groups & Alternation

• (abc) — capturing group; captures the match for abc
• (?:abc) — non-capturing group; groups without capturing
• a|b — alternation; matches a or b
• (?=abc) — positive lookahead
• (?!abc) — negative lookahead

Common Flags

• g — global; find all matches, not just the first
• i — case-insensitive matching
• m — multiline; ^ and $ match start/end of each line
• s — dotAll; . matches newlines too

Frequently Used Patterns

• Email address: ^[\w.-]+@[\w.-]+\.[a-z]{2,}$
• URL: https?://[\w.-]+(?:\.[\w.-]+)+[\w\-._~:/?#[\]@!$&'()*+,;=%]*
• IP address (v4): ^(\d{1,3}\.){3}\d{1,3}$
• Date (YYYY-MM-DD): ^\d{4}-\d{2}-\d{2}$
• Hex colour: ^#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})$
• Phone number (India): ^[6-9]\d{9}$

Using the ToolsPal Regex Tester

1. Enter your pattern in the regex field
2. Set flags (g, i, m) using the toggle buttons
3. Paste your test string in the input area
4. All matches are highlighted in real time with capture group details shown below