Regex.ai is a free web tool from Liberty Labs for building regular expressions from examples. The user pastes text into a box that holds up to 4,000 characters, drags the cursor over the strings that should match, clicks any highlight to remove it, and presses Run. Four agents then return a candidate pattern each, with the matches it finds in the text. The About page describes them in general terms: Agent A mimics the human thought process to generalise the highlights, Agent B finds a pattern from the highlights and the text, Agent C finds the pattern for adjacent single characters, and Agent D focuses on the number and type of characters. A documentation page teaches regex basics, and the site links a Discord community and a merch shop.
Read the outputs as suggestions. In the sample on the homepage the four agents return four different patterns, and they do not all match the same set of strings, so the right one has to be picked and tested on real data, including edge cases and inputs that could make a pattern slow. The site does not name an AI model or say how the agents work beyond those short descriptions, and the copyright line reads 2026. The privacy policy names Google AdSense and Google Analytics and says data is kept only as long as necessary, so avoid pasting passwords, keys or personal records into the box.
There is no paid plan on the pages reviewed. The tool is free and appears to be supported by advertising, and no API or account is mentioned.
