A fast, zero-clutter regex sandbox. Test pattern matches, inspect capture groups, test string substitutions, explain syntax tokens in plain English, and export code in 8 programming languages. Zero data sent to servers.
$1
$2
$&
$`
$'
$$
// Code snippet will be generated hereA categorized guide to character classes, anchors, quantifiers, lookarounds, and flags. Click any token to insert directly into your active pattern.
Processing happens strictly on your local machine using client-side primitives. Your data is never transmitted, tracked, or stored by Redsite.
Everything you need to author, inspect, test, and integrate regular expressions into production software.
Compiles and tests expressions instantaneously using the native ECMAScript V8 regular expression engine directly inside your browser.
Examine numbered capture groups, named groups, match character ranges, and individual substring offsets at a single glance.
Deconstruct cryptic patterns into step-by-step human explanations. Understand anchors, lookaheads, and quantifier behaviors immediately.
Preview search-and-replace transformations with full backreference support ($1, $&, and $<name>) before deploying to production.
Export boilerplate implementation code in JavaScript, TypeScript, Python, PHP, Go, Rust, Java, C#, and Bash/Ripgrep with a single click.
Your confidential strings, customer data, and proprietary tokens never leave your browser. Works fully offline as a standalone PWA.
Effortlessly validate your regex patterns from idea to production implementation.
Enter your regular expression between the slashes. Toggle flags like global (g), case-insensitive (i), or multiline (m) from the pill dropdown.
Paste the sample log, document, or dataset into the test string pane. Matches are highlighted instantly with distinctive colors.
Review the Match Inspector table to verify captured substrings, check boundaries, and read the plain-English explanation.
Generate native code snippets in Python, Go, JS, or Rust, or copy a persistent URL hash link to share your regex with team members.
No. Redsite tools run 100% locally in your browser. All pattern compilation, text matching, and group inspection execute via client-side JavaScript. No test strings or patterns are ever transmitted over the network or saved to any server.
This tester uses the modern ECMAScript (JavaScript) RegExp engine built into the browser. It features lookahead ((?=...)), lookbehind ((?<=...)), named capture groups ((?<name>...)), unicode property escapes, and the latest standard specifications.
Flags change how regular expressions evaluate:
• g (global): Finds all matches throughout the text rather than halting after the first match.
• i (ignore case): Case-insensitive matching.
• m (multiline): Causes ^ and $ to match line boundaries in addition to string boundaries.
• s (dotAll): Allows the wildcard . to match newline characters (\n).
• u (unicode): Enables full Unicode handling and surrogate pair parsing.
In the Substitution tab, you can reference captured subpatterns using $1, $2, etc. For named groups, use $<name>. Use $& to refer to the whole matched string, and $$ to insert a literal dollar sign.
Catastrophic backtracking occurs when ambiguous, deeply nested quantifiers (such as (a+)+$) cause non-deterministic polynomial time execution, potentially freezing the browser. Redsite limits execution loop steps and catches exceptions to ensure the interface remains smooth and responsive.
Yes. Once this page is loaded, all scripts and styles reside in browser cache. It functions with complete capability even when disconnected from the internet.