What is Regular expression?
A regular expression (regex) is a pattern that describes a set of strings, used to search, match, validate and replace text. Built from literal characters and special metacharacters (like . * + ? [ ] ( )), it is supported by virtually every programming language and text editor.
Regex combines literals with metacharacters: . matches any character, */+/? are quantifiers, [...] is a character class, ( ) groups, and ^/$ anchor to start/end. For example ^\d{3}-\d{4}$ matches a 7-digit phone number.
Regexes power form validation (emails, URLs), search-and-replace, log parsing and tokenizing — but complex patterns can be hard to read, so keep them documented.
Regular expression tools
Regex Data Generator
Generate 1–100 strings that match any regex pattern. Great for test data, fixtures, and fuzzing.
Open toolJSONPath Tester
Test JSONPath expressions against your JSON. Live evaluator with path and value results, filters, slices, recursive descent.
Open toolXPath Tester
Test XPath expressions against XML or HTML using your browser's native XPath engine. Live results table.
Open toolFrequently asked questions
What is regex used for?
Searching, matching, validating and replacing text — e.g. validating emails, extracting fields from logs, or find-and-replace in editors.
Are regular expressions the same in every language?
Mostly — the core syntax is shared, but flavours differ in advanced features (lookbehind, named groups, Unicode). Most follow the PCRE-style standard.