About Regex Cheat Sheet
This tool provides categorized regex syntax references with examples and a built-in tester for quick pattern building.
Key Features
- Categorized Reference: Character classes, quantifiers, groups, and assertions.
- Example-first Learning: Each rule includes practical examples.
- Live Test Panel: Try pattern + flags and inspect matches instantly.
- Flag Support: Common flags like
g,i,m,s, andu.
Recommended Workflow
- Define your goal (validate, extract, or replace).
- Build base patterns with classes + quantifiers.
- Add groups, boundaries, or assertions for precision.
- Validate edge cases in the test panel.
Common Syntax Examples
| Pattern | Meaning | Example |
|---|---|---|
\\d+ |
one or more digits | extract 123 |
^[a-z]+$ |
lowercase letters only | username validation |
| `(foo | bar)` | alternation |
(?<=@)\\w+ |
positive lookbehind | extract email segment |
FAQ
Are regex rules identical across languages?
Not exactly. JavaScript, Python, and Java differ in support for assertions, named groups, and engine behavior.
Why does a pattern work here but fail in production?
Usually due to runtime version, regex engine differences, or unsupported flags/features.