Regex Cheat Sheet: Essential Patterns for Developers

Quick Answer

Quick Answer: Start with anchors ^ and $, use character classes like \d and \w, and test interactively in our Regex Tester. Patterns below cover 80% of day-to-day tasks.

Anchors and quantifiers

Patterns you'll use weekly

Email (simple)

[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}

URL

https?:\/\/[\w\-]+(\.[\w\-]+)+[/#?]?.*

Date ISO (YYYY-MM-DD)

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

UUID

[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}

Paste any pattern into the Regex Tester and toggle flags (i case-insensitive, g global).

Flags that matter

• i — case insensitive matching
• g — find all matches, not just the first
• m — ^ and $ match line boundaries

Pitfall: catastrophic backtracking

Nested quantifiers like (a+)+ on long strings can freeze the browser. Prefer specific character classes and test on small samples first.

Try It Yourself

Test your regex live →

Frequently Asked Questions

What is the difference between . and \.?

. matches any character (except newline). \. matches a literal dot.

Do I need to escape slashes in JavaScript regex?

In /pattern/ literals, forward slashes must be escaped. In new RegExp("pattern") strings, escape backslashes: "\\d+".

When should I avoid regex?

Parsing HTML, JSON, or nested structures with regex alone—use a proper parser instead.