Regex Cheat Sheet for Everyday Debugging

Regular expressions are one of those tools where a 20-minute investment saves hours every month. Here's the subset that covers 90% of real-world use.

Character classes

• \d — digit ([0-9])
• \w — word char ([A-Za-z0-9_])
• \s — whitespace
• [^...] — negation
• . — any character except newline (add s flag to include newline)

Anchors

• ^ — start of string (or line in multiline mode)
• $ — end of string (or line in multiline mode)
• \b — word boundary

Quantifiers

• * — 0 or more
• + — 1 or more
• ? — 0 or 1
• {n} / {n,m} — exact count / range
• Add ? to any quantifier for lazy matching (shortest match)

Groups and lookarounds

• (abc) — capturing group
• (?:abc) — non-capturing group
• (?<name>abc) — named group (ES2018+)
• (?=abc) — positive lookahead
• (?!abc) — negative lookahead
• (?<=abc) — positive lookbehind
• (?<!abc) — negative lookbehind

Patterns you'll actually use

# Email-ish (pragmatic, not RFC-correct)
[\w.+-]+@[\w-]+\.[\w.-]+

# URL-ish
https?://[\w.-]+(?:/[\w\-./?%&=]*)?

# IPv4
\b(?:\d{1,3}\.){3}\d{1,3}\b

# Semver
\b\d+\.\d+\.\d+(?:-[\w.-]+)?\b

Flags

• g — global (find all matches)
• i — case-insensitive
• m — multiline (^$ match line boundaries)
• s — dot matches newline
• u — unicode

Test your patterns interactively with our regex tester before committing them to code.