RegexRegex vs Retest

RegexRegex is a free browser-based tool for building and testing regular expressions. Its checker runs JavaScript patterns in the browser and shows matches, captures, explanations, and errors, with previews for replacement text. A guided builder composes 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 an equivalent visual layout. Python, PHP, Java, .NET, and Perl engines can be used by explicitly pressing Run, which sends checks to an online execution service. Replacement previews recognize numbered and named captures such as $1 and $. The 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 include the selected pattern, engine, flags, and operation; test and replacement text are omitted unless users opt in. A cached JavaScript checker may work offline, while checks using other engines need the online service.

Retest is a free, open-source terminal utility for developing and checking regular expressions on Linux. A subject string can be supplied as an argument or piped through standard input, so it can fit into shell workflows. Retest finds all non-crossing matches and highlights nested capture groups in colors distinct from the whole match. An optional formatted list shows match order and string indexes. Release 0.2.2 added a flag for reading the subject from a file. The project provides Linux release binaries, including a 64-bit Debian installer listed for release 0.2.2. Its README describes compiling from source with Cargo and installing through a Makefile. The source code and documentation are licensed under Apache License 2.0. The project presents Retest as a terminal-based alternative to regex101, for developers building and checking patterns. No paid plans or usage limits are listed.