Common subset of PCRE, JavaScript, and Python. Language-specific features noted with flavor tags.

Yes — plus capture vs non-capture groups, backreferences, and how they work across languages.

Catastrophic backtracking?

Yes — the patterns to avoid (nested quantifiers, overlapping alternations) and safer alternatives.

Unicode character properties?

Covered — \p{L}, \p{N}, \p{Emoji}. Supported in modern JS (with u flag), Python re (with third-party regex module), PCRE natively.

A worked example, rendered from real sample data. Sign in to run the tool on your own input.

Input

digit

Output

── Character classes ──
\d   digit [0-9]
\D   non-digit

Character classes, quantifiers, anchors, groups, flags. Part of the DevTools Surf developer suite. Browse more tools in the Cheatsheets collection.

Regular expressions were invented by mathematician Stephen Kleene in 1951 and first implemented in a computer by Ken Thompson in 1968.
The POSIX standard defines two regex flavors: Basic Regular Expressions (BRE) and Extended Regular Expressions (ERE), which differ in metacharacter escaping.
Catastrophic backtracking in regex can cause a single pattern to take exponential time — the Cloudflare outage on July 2, 2019, was caused by exactly this bug.

Which flavor?: Common subset of PCRE, JavaScript, and Python. Language-specific features noted with flavor tags.
Named groups?: Yes — plus capture vs non-capture groups, backreferences, and how they work across languages.
Catastrophic backtracking?: Yes — the patterns to avoid (nested quantifiers, overlapping alternations) and safer alternatives.
Unicode character properties?: Covered — \p{L}, \p{N}, \p{Emoji}. Supported in modern JS (with u flag), Python re (with third-party regex module), PCRE natively.

A worked example, rendered from real sample data. Sign in to run the tool on your own input.

Input

digit

Output

── Character classes ──
\d   digit [0-9]
\D   non-digit

Character classes, quantifiers, anchors, groups, flags. Part of the DevTools Surf developer suite. Browse more tools in the Cheatsheets collection.

Regular expressions were invented by mathematician Stephen Kleene in 1951 and first implemented in a computer by Ken Thompson in 1968.
The POSIX standard defines two regex flavors: Basic Regular Expressions (BRE) and Extended Regular Expressions (ERE), which differ in metacharacter escaping.
Catastrophic backtracking in regex can cause a single pattern to take exponential time — the Cloudflare outage on July 2, 2019, was caused by exactly this bug.

Which flavor?: Common subset of PCRE, JavaScript, and Python. Language-specific features noted with flavor tags.
Named groups?: Yes — plus capture vs non-capture groups, backreferences, and how they work across languages.
Catastrophic backtracking?: Yes — the patterns to avoid (nested quantifiers, overlapping alternations) and safer alternatives.
Unicode character properties?: Covered — \p{L}, \p{N}, \p{Emoji}. Supported in modern JS (with u flag), Python re (with third-party regex module), PCRE natively.