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Supported formats

Input: select, text, boolean
Output: text

Privacy

Runs entirely in your browser. Your input is never uploaded, stored, or sent to a third party.

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Privacy level: Browser only

Generated the pattern /^(?:[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,})$/i.

How it works

Selected the curated Email address pattern.
Anchored the pattern to the whole string.
Composed the flags "i".
Verified the pattern has no nested quantifiers, backreferences or lookbehind.

^(?:[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,})$

Curated patterns are reviewed linear-time grammars.
The generator does not infer patterns from example text, because inference can produce dangerous backtracking.

Methodology

Select a reviewed pattern from the curated catalogue, or escape the custom literal.
Wrap the pattern in a non-capturing group and add anchors when requested.
Compose the i, g and m flags from the selected options.
Confirm the result contains no nested quantifier, backreference or lookbehind.

Usage

Choose a pattern kind, or custom-literal and enter the literal text.
Choose anchors and flags.
Run the tool, then copy the pattern and flags into your code.

Examples

These are examples, not current values: they use fixed inputs, while the interactive tool computes live results in your browser.

Anchored email

{
  "kind": "email",
  "literal": "",
  "anchors": true,
  "caseInsensitive": true,
  "global": false,
  "multiline": false
}

Escaped literal

{
  "kind": "custom-literal",
  "literal": "a.b*c",
  "anchors": true,
  "caseInsensitive": false,
  "global": false,
  "multiline": false
}

Global UUID

{
  "kind": "uuid",
  "literal": "",
  "anchors": false,
  "caseInsensitive": false,
  "global": true,
  "multiline": false
}

Limitations

Safe by construction

A generator that emits arbitrary patterns can hand you a regular expression that hangs on hostile input. Keeping the catalogue small and reviewed, and escaping custom literals exactly, removes that class of failure.

Frequently asked questions

What is ReDoS?: Regular expression denial of service is caused by patterns that can backtrack exponentially on certain input, such as nested quantifiers. The curated patterns avoid that shape and are reviewed as linear-time.
Why not generate a regex from my sample strings?: Inferring a pattern from examples tends to produce broad, backtracking-prone expressions. This tool favours a small set of reviewed safe patterns and an exact escaped literal instead.

Sources

ECMA-262: ECMAScript Language Specification — RegExp — Ecma International
MDN Web Docs — RegExp — Mozilla
OWASP — Regular expression Denial of Service — OWASP

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