Regex Tester

Regex tester for building, testing, and debugging regular expressions

A regex tester turns trial‑and‑error into fast iteration. Instead of writing a pattern, running it in code, and squinting at a boolean result, you type the pattern and test string side by side and see every match highlighted immediately. This regex tester works in the browser — no upload, no account. It supports flags (global, case‑insensitive, multiline, dotall) and highlights each capture group in a different color so you can see which part of the pattern captured what.

The two‑panel layout puts the regex pattern on the left and the test string on the right. Matches appear below with group breakdowns. Invalid patterns show the exact error position rather than a generic "bad regex" message.

Who uses it

• Frontend and backend developers — build and test form‑validation patterns, URL‑routing rules, and data‑extraction regex before committing them to code.
• QA and data engineers — extract IDs, emails, dates, IP addresses, or error codes from log files and structured text.
• SEO and content teams — test redirect‑rule patterns and URL‑rewrite expressions before applying them in .htaccess, nginx, or a CMS.
• Instructors and students — learn regex concepts like greedy vs. lazy quantifiers, lookaheads, and capture groups with immediate visual feedback.

How to use it well

1. Type or paste the regex pattern in the top field. Enable flags (g, i, m, s) via the checkboxes below the input as needed.
2. Paste the test string in the second field. Matches highlight in real time as you edit either field.
3. Use capture groups — parentheses — when you need to extract specific parts of a match, not just confirm a match exists.
4. Copy the working pattern into your code. Keep a few test strings in a comment next to it so future readers understand what the pattern matches.

Practical tips

• Test with both matching and non‑matching examples. A pattern that matches all your positives may also match strings you did not intend.
• Use the multiline flag (m) when testing against text with line breaks — ^ and $ behave differently in multiline mode.
• Escape literal dots, parentheses, and brackets with backslashes when they are part of the data rather than regex syntax.
• Check greedy vs. lazy quantifiers — .* consumes as much as possible, while .*? stops at the first valid next token.

Common use cases

• Validating form input — email, phone number, postal code, credit‑card number format
• Extracting structured data from unstructured text — dates, IDs, URLs, error codes
• Debugging redirect rules and URL‑rewrite patterns before deploying to production
• Parsing log files — extract timestamps, IP addresses, user IDs, and status codes
• Teaching and learning regex — immediate visual feedback makes quantifiers, anchors, and groups tangible

Privacy and browser‑side processing

All pattern matching runs locally in the browser. Your test strings — which may include production log samples, internal URLs, or customer‑data fragments — never leave your device. For production secrets and regulated data, sanitise the test input before pasting into any browser tool.

Related searches and tools

People who use this regex tester often also need JSON Formatter (inspect structured payloads you extracted with regex), SQL Formatter (clean up queries for code review), and Character Counter (check the length of extracted values). All three run in‑browser.