Regex Tester
Enter a regular expression and flags to highlight matches in the test string below in real time and see the match list. All processing happens in your browser, so your input is never sent out.
How to use
Enter a regex and flags (g, i, m, s, etc.) and a test string below; matches are highlighted in yellow and the list of matched strings appears.
Frequently asked questions
What regex syntax is supported?
It uses the browser's JavaScript regular expressions (RegExp) directly. The g, i, m, s, u, and y flags are supported.
Are the values I enter sent to a server?
No. All processing happens inside your browser, and the regex and text you enter are not sent to any external server.
Practical example and verification criteria
Regex Tester: First identify whether the source is plain text, a URL component, JSON, CSV, CSS, JavaScript, a color, or a token, then check character encoding, delimiters, quoting, and line-ending rules. Encoding is not encryption, decoding is not signature verification, and minification is not code optimization; define the required output format and destination before running the tool.
Regex Tester: For a quick check, start with ^\d{4}$ ↔ 2026 as a small input whose result relationship you can verify directly. Confirm that the input summary, units, and options match your intent before applying the tool to real values or a copy of the source; this reduces setup mistakes.
Regex Tester: Put the output into the target browser, build tool, API, or design surface and check for parsing errors or changed meaning. Decoding does not prove authenticity, a hash cannot be decrypted, and minified code is not guaranteed to behave like the source. Preserve the original and tests, and avoid entering passwords, tokens, or personal data.
Regex Tester · Work record: For real work, record the input conditions, selected options, and result together. Do not assume the same state will remain after a refresh or device change. Preserve important results separately using copy, download, a screenshot, or another method the page supports, then reopen them in the target environment.
Regex Tester · Error check: If an error or unexpected result appears, reduce the input, run again with default options, and then change one condition at a time. Recording error messages and boundary values helps distinguish format issues, unsupported cases, and browser resource limits, and prevents an empty result from being mistaken for success.
Regex Tester · Scope of use: Check the page guidance for browser processing versus server lookup, storage location, and supported scope. Use sensitive source material or secrets only when strictly necessary. High-impact work such as legal, financial, or medical decisions or changes to an operational system requires current authoritative information and a separate verification process.