Regex Tester

A regular expression describes a pattern that a regex engine matches against text, character by character, using rules like literal characters, character classes, quantifiers for how many times something can repeat, and anchors for positions like the start or end of a string. Flags change how that matching behaves — g finds all matches instead of stopping at the first, i ignores case, m changes how ^ and $ behave across multiple lines, and s lets . match newline characters as well.

Regex shows up constantly in real development work: validating input formats like email addresses or phone numbers, extracting specific substrings from log lines or scraped text, or performing search-and-replace operations that are too irregular for a plain string match. Testing a pattern interactively against real sample text, rather than only against a handful of manual test cases in code, makes it much faster to catch cases the pattern doesn't handle the way you expected.

Regex has real limitations worth knowing: it works on flat, linear text and struggles with recursive or deeply nested structures, which is why parsing HTML or JSON with regex alone is a well-known bad idea, and pattern behavior can subtly differ between regex engines such as JavaScript's, PCRE, or Python's re module. A pattern tested here should still be verified in the actual language it will run in if precise behavior matters.