Complete regex cheatsheet (with copy-paste patterns that actually work)

# The fundamentals

# Character classes

| Pattern | Matches |

|---|---|

| . | Any character except newline (or anything with /s flag) |

| \d | Digit [0-9] |

| \D | Non-digit |

| \w | Word char [A-Za-z0-9_] |

| \W | Non-word |

| \s | Whitespace (space, tab, newline) |

| \S | Non-whitespace |

| [abc] | Any of a, b, or c |

| [^abc] | Anything except a, b, or c |

| [a-z] | Range |

# Anchors

| Pattern | Matches |

|---|---|

| ^ | Start of string (or line with /m) |

| $ | End of string (or line with /m) |

| \b | Word boundary |

| \B | Non-word-boundary |

# Quantifiers

| Pattern | Matches |

|---|---|

| * | 0 or more |

| + | 1 or more |

| ? | 0 or 1 |

| {n} | Exactly n |

| {n,} | n or more |

| {n,m} | Between n and m |

| *? / +? / ?? | Lazy (match as few as possible) |

# Groups

| Pattern | Meaning |

|---|---|

| (abc) | Capturing group |

| (?:abc) | Non-capturing (faster, no back-reference) |

| (?<name>abc) | Named group |

| \1 | Back-reference to group 1 |

| (?=abc) | Positive lookahead |

| (?!abc) | Negative lookahead |

| (?<=abc) | Positive lookbehind |

| (?<!abc) | Negative lookbehind |

# 30 patterns you'll actually use

<div class="callout callout-tip" role="note"><div class="callout-title">Tip</div><div class="callout-body"><p>Every pattern below is testable in-browser in our <a href="/regex-tester">Regex Tester</a> — paste the pattern and your test string, see matches highlighted live.</p></div></div>

# Numbers

• Integer: ^-?\d+$
• Positive integer: ^\d+$
• Float (with or without sign): ^-?\d+(\.\d+)?$
• Percentage: ^(100|\d{1,2}(\.\d+)?)%$
• Currency: ^\$?\d+(,\d{3})*(\.\d{2})?$

# Dates and times

• ISO 8601 date: ^\d{4}-\d{2}-\d{2}$
• ISO 8601 datetime: ^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}(\.\d+)?(Z|[+-]\d{2}:\d{2})?$
• Time HH:MM: ^([01]\d|2[0-3]):[0-5]\d$
• Time HH:MM:SS: ^([01]\d|2[0-3]):[0-5]\d:[0-5]\d$

# Email + web

• Email (practical): ^[^\s@]+@[^\s@]+\.[^\s@]+$
• URL: ^https?:\/\/[^\s/$.?#].[^\s]*$
• Domain: ^(?:a-z0-9?\.)+[a-z]{2,}$
• Slug: ^[a-z0-9]+(?:-[a-z0-9]+)*$

# IPs

• IPv4: ^((25[0-5]|2[0-4]\d|[01]?\d\d?)\.){3}(25[0-5]|2[0-4]\d|[01]?\d\d?)$
• IPv6 (simple): ^([0-9a-fA-F]{1,4}:){7}[0-9a-fA-F]{1,4}$

# Identifiers

• UUID v4: ^[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$
• Hex color: ^#(?:[0-9a-fA-F]{3}){1,2}$
• MAC address: ^([0-9A-Fa-f]{2}[:-]){5}([0-9A-Fa-f]{2})$
• Credit card (any 13–19 digits): ^\d{13,19}$

# Strings

• Starts with a letter: ^[A-Za-z]
• Only alphanumeric: ^[A-Za-z0-9]+$
• Password: 8+ chars, letter + digit: ^(?=.[A-Za-z])(?=.\d).{8,}$
• Password strong: 12+ chars, mixed case + digit + symbol: ^(?=.[a-z])(?=.[A-Z])(?=.\d)(?=.[^A-Za-z0-9]).{12,}$

# Code

• JWT (rough shape): ^[A-Za-z0-9_-]+\.[A-Za-z0-9_-]+\.[A-Za-z0-9_-]*$
• Hex string: ^[0-9a-fA-F]+$
• Base64 (with padding): ^[A-Za-z0-9+/]*={0,2}$
• Markdown link: \[([^\]]+)\]\(([^)]+)\)

# HTML-ish

• Strip HTML tags (replace with empty): <[^>]+>
• Extract src attribute: src="'["']
• Extract first heading: <h1[^>]>([\s\S]?)<\/h1>

# Whitespace

• Trim whitespace (replace both sides): ^\s+|\s+$
• Collapse runs of whitespace: \s+ (replace with " ")

# Flags reference

| Flag | Name | Use |

|---|---|---|

| g | Global | Find all matches, not just first |

| i | Ignore case | Case-insensitive |

| m | Multiline | ^ / $ match line ends |

| s | dotAll | . matches newlines |

| u | Unicode | Handle surrogate pairs, \u{10FFFF} |

| y | Sticky | Anchor each match at lastIndex |

# Debugging regex

• Build in small pieces; add one group at a time.
• Name your captures: (?<year>\d{4})-(?<month>\d{2}) — reads itself.
• Catastrophic backtracking: nested quantifiers like (a+)+b can hang on aaaaaaaac. Avoid.
• When in doubt, paste into our Regex Tester — the live highlighting makes mistakes obvious.

# Related tools

• Regex Tester — test patterns live
• Slug Generator — regex-based URL normalization