Which regex flavor is this?

JavaScript (the same engine as your browser). Most syntax transfers to Python, Java and PCRE, but lookbehind and some advanced features differ between flavors - always re-test in your target language.

Why is my pattern marked invalid?

The error message shows the browser's exact complaint - usually an unclosed bracket, a stray backslash, or a bad quantifier. Fix it in the pattern box and highlighting resumes instantly.

What's the difference between the g and m flags?

g (global) finds all matches instead of stopping at the first. m (multiline) makes ^ and $ match at line boundaries, not just the string's start/end. They're independent - you often want both.

How do capture groups work here?

Parentheses create numbered groups. Each match row expands to show group 1, 2, 3… with their captured text - use (?:…) for non-capturing groups when you don't need the value.

Is catastrophic backtracking a risk?

In this tester, a runaway pattern just freezes your tab briefly - close it if needed. In production code, avoid nested quantifiers like (a+)+ and prefer atomic groups or possessive quantifiers where your flavor supports them.

Developer Tools

Testador de Regex

Regex não corresponde e você não consegue entender por quê? Cole seu padrão e a string de teste - as correspondências acendem ao vivo enquanto você depura.

Pattern (without the / slashes /)

Flags

Test string

Common patterns

Regex cheatsheet

Character classes

.: Any character except newline
\d / \D: Digit / non-digit
\w / \W: Word char (A-Za-z0-9_) / non-word
\s / \S: Whitespace / non-whitespace
[abc]: Any of a, b, c
[^abc]: Anything except a, b, c
[a-z]: Range a through z

Quantifiers

*: 0 or more (greedy)
+: 1 or more (greedy)
?: 0 or 1
{n}: Exactly n
{n,}: n or more
{n,m}: Between n and m
*? +? ??: Lazy versions: match as little as possible

Anchors

^: Start of string (or line with m flag)
$: End of string (or line with m flag)
\b: Word boundary
\B: Not a word boundary

Groups

(abc): Capture group: numbered 1, 2, 3…
(?:abc): Non-capturing group
(?<name>abc): Named capture group
a|b: Alternation: a or b
\1: Backreference to group 1
(?=abc): Positive lookahead
(?!abc): Negative lookahead

Private by design: This tool runs entirely in your browser. Nothing you type or upload is sent to a server.

Como usar Testador de Regex

Insira seu padrão. Digite o regex sem barras e alterne os sinalizadores (g, i, m, s, u) conforme necessário.
Adicione o texto de teste. Cole a string com a qual você está comparando - logs, entrada de formulário, seja lá o que for.
Inspecionar correspondências. Correspondências destacadas no texto; o painel abaixo lista cada correspondência com seus grupos de captura.
Tentar uma predefinição. Travou? Carregue um padrão comum (e-mail, URL, data…) e adapte-o.