Regex Tester
A regex tester lets you try a regular expression on sample text and see what it matches. Type a pattern, choose flags, paste your text, and this free tool highlights every match, lists capture groups and previews replacements. It runs JavaScript regular expressions and stops any pattern that takes too long, so your page never freezes.
Enter your JavaScript regex pattern and select flags.
$1, $&, $<name>| # | Index (Range) | Full Match | Capture Groups | Named Groups |
|---|
Paste plain text to escape characters like . * + ? ^ $ { } ( ) | [ ] \ so it matches literally:
What is a regex tester and when should you use it?
A regular expression is a short pattern that describes text, such as "any number" or "a word at the start of a line". Testing it on sample text before using it saves time and mistakes. This tester uses JavaScript's own RegExp engine; servers such as Apache and nginx and languages such as Python or PHP use different engines (such as PCRE), so complex patterns may need small adjustments. In website development and technical SEO, regular expressions power URL rewrite rules, log parsing scripts, redirect maps, and analytics filters. For Apache web server rules, build directives with the .htaccess Redirect Generator, and for NGINX servers, use the Nginx Redirect Generator. Convert bulk URL migration lists with the Bulk Redirect Formatter, audit redirect paths with the Redirect Map Checker, and validate URL mappings via the Old vs New URL Mapping Validator. If you are cleaning plain text lists or keyword clusters, try the Line Sorter and Deduplicator or List Compare. You can also clean tabular datasets with the CSV Deduplicator, inspect query parameters and paths using the URL Parser, and evaluate page content with the Duplicate Content Similarity Checker.
How do you use it?
- Type your regular expression pattern without enclosing slashes.
- Choose the regex flags you need (global, ignore case, multiline, dotAll, indices).
- Paste your test string or sample data into the text area.
- View matched tokens, capture groups, and match offsets in real time.
- Switch to Replace or Split modes if you need substitution or tokenization previews.
Working on a comprehensive technical audit? Browse all free SEO tools to discover the next step in your workflow, or contact our technical support team if you require a specialized custom utility.
Result interpretation & practical applications
When evaluating the output of the regex tester, review the parsed metrics against your specific site architecture. Outputs are formatted for direct implementation into your HTML source, web server configuration, or Google Search Console audit files.
Always inspect generated values for contextual nuance. Automated tools highlight structural patterns, but manual verification confirms that technical directives align with your overarching SEO strategy.
Technical rules and limitations
- Patterns follow the standard ECMAScript JavaScript regular expression specification.
- Slow or backtracking patterns are safely stopped by a background Web Worker time limit to prevent browser freezing.
- Results in other software can differ slightly because Apache mod_rewrite, nginx, and PCRE implement distinct syntax extensions.
Official regular expression rules and syntax are documented in MDN's guide to regular expressions and the RegExp reference.
Common mistakes and troubleshooting
- Forgetting the global (g) flag and only finding the single first match in your test text.
- Failing to escape special characters like dots, brackets or question marks (e.g., using "example.com" instead of "example\.com").
- Assuming a JavaScript regex works identically in Apache .htaccess or nginx configuration without testing engine variations.
No tool can promise how a search engine will crawl, index, or rank your pages. This tool generates and validates code against documented technical specifications; you determine where to deploy it, and you should always test changes on staging environments first. Google publishes extensive guidelines in Search Central on evaluating third-party SEO tools and advice. Learn more about our technical testing standards on our about us page, or explore full site audits on our pricing page.
Related free tools & workflows
Browse all Advanced SEO, Migration & Quality Assurance Tools →Technical SEO Audit Workflows
Indexability & Crawling
Redirects & HTTP Headers
Authoritative Technical Documentation & Standards
This tool executes logic aligned with official technical documentation and search engine webmaster standards:
- MDN Web Docs regular expressions guide
MDN Web Docs: JavaScript Regular Expressions Guide
Primary engineering source and technical documentation.
- ECMAScript RegExp Specification
ECMA International: ECMAScript RegExp Objects Specification
Primary engineering source and technical documentation.
Regex Tester questions
Which regex flavour does this tool use? ↓
This tester executes native JavaScript (ECMAScript) regular expressions directly in your browser.
Why did my pattern stop with a timeout message? ↓
The pattern exceeded your execution time limit. This typically occurs when catastrophic backtracking happens on nested repeating quantifiers.
Can I test replacement strings and capture groups? ↓
Yes. Switch to Replace mode to preview substitutions using $1, $2, $&, and named capture groups ($
Is this tool free? ↓
Yes. It is completely free to use and requires no registration or subscription.
Does this tool visit my website or store my files? ↓
No. It executes entirely in your local browser runtime. Your inputs and results are never stored or logged on our servers.
Ready for the next step in your audit?
ToxicBacklink – Free SEO Tools & Backlink Checker builds fast, browser-based utilities for webmasters, developers, and SEO professionals. Each tool executes locally, shows exact modifications, and follows published specifications. Read more about us, check our how it works guide, browse all tools, or return to the home page.