RegexRegex

RegexRegex is a free browser-based tool for building and testing regular expressions. Its checker runs JavaScript patterns locally and displays matches, captures, explanations, and errors, with previews for replacement text. A guided builder assembles basic JavaScript patterns using controls for character types, quantities, groups, boundaries, and flags; it can test the pattern it creates, but does not cover every syntax feature or convert arbitrary patterns into equivalent visual layouts. Python, PHP, Java, .NET, and Perl checks are available through an online execution service after the user explicitly presses Run. Replacement previews recognize numbered and named capture references such as $1 and $. A searchable reference covers 25 syntax and flag items. Users can save up to 50 test cases in the browser, each with input up to 20,000 characters. Share links keep test and replacement text out unless users opt in. A cached JavaScript checker may work offline, while checks using other engines require the online service.

RegexRegex combines a local JavaScript checker with a guided builder and optional online runtimes. Its builder has defined limits, and checks beyond JavaScript depend on the online service.

RegexRegex suits people who want to test JavaScript expressions in a browser, or compose basic patterns with guided controls. It can also serve users checking other supported engines when they can use the online execution service.

RegexRegex is a free browser-based workspace for developers and learners who mainly need to build and check JavaScript regular expressions. Its local checker and guided controls are useful for common patterns, but the builder is deliberately limited and other engine checks require an online run.

Overview

The JavaScript checker tests matches and captures, previews replacements, and explains patterns and errors. Because JavaScript checks run in the browser, RegexRegex is a practical choice for iterating on that engine without sending each check to its execution service. Python, PHP, Java, .NET, and Perl are also supported, but their checks run through an online service only after you press Run; this is less suitable for offline work or workflows that need every engine to execute locally.

Key features

Guided building and reference

Controls for character types, quantities, groups, boundaries, and flags help assemble basic JavaScript RegExp patterns, which users can then inspect and test. This is a useful route into common expressions, particularly for learners, but it is not a visual editor for every regex syntax: it neither covers every feature nor converts arbitrary patterns into equivalent visual trees. A searchable cheat sheet with 25 syntax and flag items offers a compact reference alongside the builder.

Testing and saved cases

Replacement previews handle numbered and named capture references, including $1 and $<name>. Users can save up to 50 test cases in the browser, with each test input limited to 20,000 characters. These caps suit personal pattern work, but they may constrain larger test collections or unusually long inputs.

Sharing and data handling

Share links put the selected pattern, engine, flags, and operation in the URL fragment. Test and replacement text stay out unless the user opts to include them, making sharing more deliberate. The maker says the native execution service does not record or persist submitted input. Separately, Cloudflare Web Analytics may collect page and device information, and Google Analytics 4 may use analytics cookies if enabled.

A cached JavaScript checker may work offline; checks using the other engines depend on the online service. Python and PHP reference snippets are also provided, but they do not execute unless a native engine run is explicitly requested. The maker describes no external integrations.

Pricing

The Free online regex tester costs free. It includes browser-based JavaScript checks and access to Python, PHP, Java, .NET, and Perl through an explicit online run. There is no paid tier described, so this is a straightforward fit for individuals who can work within the saved-case and input-length caps. Readers who need offline execution across engines or a builder covering the full regex syntax should look elsewhere rather than expect a higher RegexRegex plan to remove those limits.

Platforms

RegexRegex is a web tool. JavaScript checks may continue to work from a cached checker offline, but the other engine runs require an internet connection to reach the execution service.

Who it's for

RegexRegex suits learners constructing common JavaScript patterns and developers who want a browser-based place to inspect matches, captures, replacements, explanations, and errors. It is less appropriate for users who need arbitrary expressions reverse-parsed into a visual builder, extensive saved test collections, or offline checks in Python, PHP, Java, .NET, or Perl.

Pros and cons

• Pro: JavaScript checks run locally, with match, capture, replacement, explanation, and error views together.
• Pro: Guided controls and a searchable 25-item reference help with common JavaScript syntax.
• Pro: Share links exclude test and replacement text by default, and the maker says native-run input is not recorded or persisted.
• Con: The builder covers basic patterns rather than every syntax feature and cannot turn arbitrary patterns into equivalent visual trees.
• Con: Non-JavaScript checks need an explicit online run, so those engines are not available offline.
• Con: Browser-saved cases top out at 50, and test inputs at 20,000 characters.

Alternatives

Regular Expression Testers is a broader category list for readers who want to compare more tools.

• AppTools Regex Tester is a better candidate for readers who want a free utility across Android, iOS, Linux, macOS, web, and Windows, with no sign-up or subscription.
• Debuggex is worth considering when regex visualization and debugging are priorities; its free plan includes a visualizer, debugger, and two saved unit tests, with Python and PCRE engines free while in beta.
• regex101 is an alternative to consider for readers seeking a freemium regex tool; its free plan is priced as free.
• RegexCraft is an option for readers looking for a free personal, hobby, learning, or side-project tool on Linux, macOS, or Windows.
• RegexPilot may suit readers who want JavaScript and TypeScript engines free on macOS, the web, or as an extension, with a one-time license option for all 21 flavors.
• RegExr is another free web tool for regex learning, building, and testing.
• The Regex Coach is an option for readers seeking a free Linux or Windows program.
• Regex Shuttle is another free web option, with a plan described as having no account, limits, or ads.

Verdict

Choose RegexRegex if you want a free, browser-based JavaScript checker with guided help, useful replacement previews, and an optional path to several other engines. Its local JavaScript workflow is the main reason to choose it; look elsewhere if you need the builder to handle arbitrary syntax or need non-JavaScript checks to work offline.