Overview
The Regex Generator & Tester helps you compose regular expressions, toggle flags, and validate patterns against sample text with instant highlighting. Everything runs inside your browser, works offline, and respects your privacy. When you are ready, export your pattern, flags, and examples to files you can share or commit.
Quick facts
- No servers, logins, or analytics. All processing is client-side.
- Flags and tokens are selectable, and matches are highlighted in real time.
- One-click export saves JSON and TXT bundles via the browser’s download prompt.
Why it matters
Regular expressions are powerful, but trial-and-error in code can be slow and risky. A local, visual builder makes patterns easier to understand and safer to refine before deployment. Keeping everything on-device protects sensitive sample data, which is especially important for logs, emails, or personally identifiable information.
How it works
The page uses the browser’s native RegExp engine. As you type or insert tokens, the pattern is compiled with your selected flags. The sample text area is scanned for matches and the tool wraps matches in visual highlights. Downloads are created with the Blob API, so files are generated locally and never uploaded.
Quick start
Step-by-step
- Open the tool and type your pattern in the Pattern field or click tokens to insert common pieces.
- Select flags such as i for case-insensitive and g for global matching.
- Paste sample text into the Test area. Matches are highlighted as you type.
- Click “Add as example” to collect test strings that will be included in downloads.
- Use “Copy regex” to copy /pattern/flags or “Download” to save JSON and TXT bundles.
Flags guide
- g global, find all matches instead of just the first.
- i case-insensitive, match letters regardless of case.
- m multiline, treat ^ and $ as start and end of line.
- s dotall, make . match newline characters.
- u unicode, enable full Unicode features and escapes.
Common patterns
Examples
- Email (simple): ^[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,}$
- IPv4 address: ^(?:25[0-5]|2[0-4]\d|1?\d?\d)(?:\.(?:25[0-5]|2[0-4]\d|1?\d?\d)){3}$
- ISO date: ^\d{4}-\d{2}-\d{2}$
- Trim whitespace: ^\s+|\s+$ (use with replace)
Tips
- Prefer non-greedy quantifiers like +? and *? when matching delimited text.
- Use groups ( ) to capture and (?: ) for non-capturing.
- Escape special characters with \. \? \+ \* \| \( \) \[ \] \{ \}.
- Validate performance on large inputs, especially when using backtracking-heavy constructs.
Export and download
When you click Download in the tool, two files are generated entirely in your browser. A JSON bundle contains the pattern, flags, timestamp, and any saved examples. A TXT file includes a human-readable version for quick sharing. Both files are saved through a standard download prompt with no network requests.
Privacy and safety
The tool does not transmit your pattern, text, or examples to any server. You can use the page offline. If you are testing sensitive data, consider redacting or synthesizing examples. Always review patterns for catastrophic backtracking risks before using them in production systems.
Troubleshooting
- “Syntax error” means the engine could not compile your pattern. Check unbalanced brackets or escapes.
- If highlighting seems wrong, verify the g flag. With global off, only the first match is shown.
- Zero-length matches can loop. The tool advances the index to prevent lockups when g is enabled.
- For multiline text, try enabling m so ^ and $ match line boundaries.
Legal Disclosure
This page describes a local-only utility that compiles and tests regular expressions in your browser. No analytics or tracking is embedded on the tool page, and no data leaves your device unless you choose to download files. Use is your responsibility and must comply with applicable laws and acceptable-use rules. Validate patterns for correctness and performance before deploying them in production.