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The 10 building blocks

Symbol	Means	Example
`.`	Any character except newline	`a.c`matches "abc", "a1c"
`*`	0 or more of previous	`ab*c`matches "ac", "abc", "abbc"
`+`	1 or more of previous	`ab+c`matches "abc", not "ac"
`?`	0 or 1 of previous (optional)	`colou?r`matches "color" and "colour"
`^`	Start of string	`^Hello`only matches if starts with "Hello"
`$`	End of string	`world$`only matches if ends with "world"
`[abc]`	Any character in set	`[aeiou]` matches any vowel
`[^abc]`	Any character NOT in set	`[^0-9]` matches any non-digit
`\d`	Any digit (0-9)	`\d+` matches one or more digits
`\w`	Word character (letter, digit, _)	`\w+` matches a word

The patterns you will actually use

Email validation

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

Validates the structure of an email address. Note: this does not verify the email exists — only that it looks like a valid format. For production, send a confirmation email instead of relying on validation alone.

URL matching

/https?://[^s]+/g

Matches http:// and https:// URLs. The ?makes the 's' optional. The [^\s]+ matches everything up to whitespace.

Phone numbers (flexible)

/(+?d{1,3}[s-]?)?(?d{3})?[s.-]?d{3}[s.-]?d{4}/

Matches most international and US phone number formats. Phone number formats are famously inconsistent — consider normalizing before validating.

Numbers only

/^d+$/

Validates that a string contains only digits. Useful for ZIP codes, IDs, PINs.

Alphanumeric only

/^[a-zA-Z0-9]+$/

Strong password (8+ chars, upper, lower, digit, symbol)

/^(?=.*[a-z])(?=.*[A-Z])(?=.*d)(?=.*[@$!%*?&])[A-Za-zd@$!%*?&]{8,}$/

Uses lookaheads ((?=...)) to require each character class without specifying position.

Find all hashtags in text

/#w+/g

Matches # followed by word characters. The g flag finds all matches.

Extract content inside quotes

/"([^"]+)"/g

Captures everything inside double quotes. The capturing group ([^"]+)returns just the content without the quotes.

Trim leading and trailing whitespace

/^s+|s+$/g

Replace with an empty string to trim. Note: in JavaScript, str.trim()does the same thing more readably — use the regex when you need more control.

Match hex color codes

/#([A-Fa-f0-9]{6}|[A-Fa-f0-9]{3})/g

Matches 6-digit (#ffffff) and 3-digit (#fff) hex color codes.

Flags you need to know

g — global: find all matches, not just the first
i — case-insensitive: treat A and a as the same
m — multiline: ^ and $ match the start/end of each line, not just the whole string
s — dotAll: make . match newlines too

Summary

The patterns above cover the majority of real-world regex use. Test them with the free regex tester — paste the pattern, paste your test string, see matches highlighted in real time. For complex patterns, read them from left to right and break them into smaller pieces.