<div class="nfaf-generated-content"><div class="nfaf-visual-card" style="--nfaf-accent:#191287"><div class="nfaf-visual-icon" aria-hidden="true"><svg viewBox="0 0 64 64" role="img"><circle cx="32" cy="32" r="28" fill="currentColor" opacity=".12"></circle><path d="M20 34l8 8 17-19" fill="none" stroke="currentColor" stroke-width="5" stroke-linecap="round" stroke-linejoin="round"></path></svg></div><div><strong>Regular Expression Tester</strong><span>Browser-first utility with visible inputs, outputs, and limitations.</span></div></div><p class="nfaf-lede">This tool provides a small, visible test loop for a JavaScript pattern so users can inspect matches before placing the expression into application code.</p><p><strong>Designed for:</strong> Developers learning or debugging JavaScript regular expressions.</p><h2>How to use this tool</h2><p>Enter the pattern without slash delimiters, choose flags such as i or g, and paste representative sample text. The result lists match text, index positions, and captured groups when the browser accepts the pattern.</p><h2>How the result is produced</h2><p>The browser RegExp constructor compiles the supplied pattern. String.matchAll is used for global inspection and a single execution path is used for non-global patterns.</p><h2>Test examples</h2><p>Pattern: \b(cat|dog)\b with flag i matches cat or dog as complete words. A pattern such as ^[A-Z]{2}\d{4}$ checks a simple two-letter/four-digit sample format, but it is not a universal identifier validator.</p><h2>Limitations</h2><p>Regular expressions are code-like input. A pattern can be computationally expensive or misleading when used on untrusted text. The tester uses JavaScript regex syntax and does not validate patterns for every other programming language.</p><h2>Privacy and processing</h2><p>The pattern and sample text are evaluated in the browser. They are not transmitted by this tool.</p><h2>Related guide</h2><p><a href="https://nofyi.com/how-to-test-regular-expressions/">How to test a regular expression without overclaiming what it validates</a></p><h2>Related tools in this category</h2><ul class="nfaf-related-tools"><li><a href="https://nofyi.com/tools/json-formatter/">JSON Formatter and Validator</a><span>Paste a JSON object or array, then format it or validate its syntax.</span></li><li><a href="https://nofyi.com/tools/base64-encoder-decoder/">Base64 Encoder and Decoder</a><span>Choose encode or decode. The browser performs the conversion locally.</span></li><li><a href="https://nofyi.com/tools/timestamp-converter/">Unix Timestamp Converter</a><span>Convert a date-time to Unix seconds or convert seconds back to an ISO-style date.</span></li></ul><h2>Documentation</h2><ul><li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp" rel="nofollow noopener" target="_blank">https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/RegExp</a></li><li><a href="https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/matchAll" rel="nofollow noopener" target="_blank">https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/matchAll</a></li></ul><p class="nfaf-disclosure">This page describes the implementation shipped with the NOFYI Tool Factory. Review the interface output before using it in a production workflow.</p></div><div class="nfaf-app-slot">[nfaf_tool_app]</div>
