Regex Tester
Test regular expressions online with live match highlighting, regex flags, match count, replacement preview and copy-ready results.
This Regex Tester is built for developers, students, website owners and anyone working with patterns, validation rules, log files, form inputs, code snippets or data cleanup.
Regex Tester Tool
Enter a regular expression, paste test text and instantly see matches. Use flags, examples and replacement preview to build a cleaner pattern faster.
Pattern and Test Text
Write your regex pattern without wrapping slashes. Example: \b\w+@\w+\.\w+\b
Live Highlight Preview
Matches are highlighted below. Capture groups and match indexes appear in the match list.
Replace Preview
Use this section to test replacement output before changing real text. JavaScript-style replacements like $1, $2 and $& are supported.
Common Regex Examples
Click any example to load a useful pattern and sample text.
What Is a Regex Tester?
A Regex Tester is an online tool that helps you test regular expressions against sample text. A regular expression, often called regex, is a pattern used to find, match, validate or replace text. Developers use regex for form validation, search tools, data cleanup, log filtering, URL matching, email validation, phone number detection and many other text-processing tasks.
Instead of guessing whether a pattern works, you can paste your text into this tool and instantly see what the regex matches. The highlighted preview shows the matched parts, while the match list gives each result separately. This makes it much easier to debug patterns, understand capture groups and avoid mistakes before using the expression in code.
Regex can look confusing at first because it uses symbols like dots, brackets, backslashes, question marks and plus signs. But every symbol has a purpose. A dot can match any character. A plus sign means one or more. Brackets can define a character set. Parentheses can create capture groups. Flags can change how the pattern behaves. A good regex tester makes these patterns easier to understand because you can see the result immediately.
How to Use This Regex Tester
This Regex Tester is designed to be simple enough for beginners but useful enough for developers. You can test patterns, enable flags, highlight matches, copy results and preview replacement output in one place.
- Enter your regex pattern in the pattern box. Do not add leading and trailing slashes.
- Paste or type your sample text in the test text area.
- Choose regex flags such as global, case-insensitive or multiline.
- Click Test Regex or simply edit the text and let the tool update.
- Review the highlighted preview and match list.
- Use the replace preview if you want to test replacement output.
- Copy the regex pattern, matches or replacement result when you are done.
For example, if you want to find email addresses in a block of text, load the email example and replace the sample text with your own data. If you want to clean extra spaces, use the extra spaces example and preview replacement with one normal space.
Regex Flags Explained
Regex flags change how a regular expression behaves. The same pattern can return different results depending on which flags are enabled. This tool supports common JavaScript regex flags.
| Flag | Name | What It Does |
|---|---|---|
| g | Global | Finds all matches instead of stopping after the first match. |
| i | Case-insensitive | Matches uppercase and lowercase letters as the same. |
| m | Multiline | Makes ^ and $ match the start and end of each line, not just the whole text. |
| s | Dotall | Allows the dot character to match newline characters too. |
| u | Unicode | Enables better handling of Unicode characters in JavaScript regex. |
If you are not sure which flags to use, start with g and i. The global flag helps find every match, and the case-insensitive flag avoids missing text just because a letter is uppercase.
Common Uses for Regular Expressions
Regular expressions are useful whenever you need to search or validate text with a pattern. They are used in programming, spreadsheets, website forms, databases, analytics tools, log systems and text editors.
- Email validation: check whether a form input looks like an email address.
- Phone number detection: find phone numbers in support tickets or contact lists.
- URL matching: detect links inside text, comments or imported data.
- Data cleanup: remove extra spaces, duplicate punctuation or unwanted characters.
- Log analysis: find error codes, timestamps, IDs or IP addresses in server logs.
- Content editing: search and replace repeated patterns in articles, code or documents.
- Form validation: check usernames, postal codes, dates or custom fields.
Regex is powerful, but it should be tested carefully. A pattern that is too broad can match more than you expect. A pattern that is too strict can miss valid data. Testing with real examples helps you find the right balance.
Regex Pattern Basics for Beginners
If you are new to regular expressions, start with small patterns and build them step by step. Do not try to write a complex expression all at once. Test one part first, then add more rules as needed.
| Pattern | Meaning | Example Match |
|---|---|---|
| . | Any single character except newline, unless dotall is enabled. | a, 7, @ |
| \d | Any digit from 0 to 9. | 5 |
| \w | Word character: letter, digit or underscore. | A, z, 9, _ |
| \s | Whitespace such as space, tab or newline. | space |
| + | One or more of the previous token. | \d+ matches 123 |
| * | Zero or more of the previous token. | a* matches empty text or aaa |
| ? | Zero or one of the previous token. | colou?r matches color and colour |
| [abc] | Match one character from the set. | a, b or c |
| ^ | Start of text or start of line with multiline mode. | Start anchor |
| $ | End of text or end of line with multiline mode. | End anchor |
Regex Replace Preview
Regex is not only for finding text. It is also useful for replacing text. This tool includes a replace preview so you can test the output before applying it anywhere important.
For example, you can find extra spaces using \s{2,} and replace them with a single space. You can capture parts of a pattern with parentheses and reuse them in the replacement using $1, $2 and other group references. You can also use $& to insert the full match.
Testing replacement first is important because a wrong regex replacement can change more text than expected. Always preview the output before using a regex on important code, database exports, articles or customer data.
Tips for Writing Better Regex
- Start with a small pattern and test it before adding more rules.
- Use the global flag when you want all matches, not only the first one.
- Use case-insensitive mode when uppercase and lowercase should both match.
- Escape special characters like dots when you want the literal character.
- Use anchors like ^ and $ when the whole line must match.
- Test with both valid and invalid examples.
- Avoid making patterns too broad unless you really want loose matching.
- Preview replacements before using them on important text.
A good regex is not always the shortest regex. The best pattern is the one that matches what you need, avoids what you do not need and remains understandable later.
Privacy and Safety
This Regex Tester runs in your browser. The text you type, the pattern you test and the replacement output are processed locally using JavaScript. You do not need to create an account or upload a file to use the tool.
Even so, avoid pasting private passwords, secret API keys, confidential customer data or sensitive business information into any online tool unless you are sure it is safe for your workflow. For sensitive work, use sample text that has the same structure but does not include private data.
Related Tools
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Regex Tester FAQs
What is a regex tester?
A regex tester is a tool that lets you test a regular expression against sample text. It shows matches, highlights results and helps you debug the pattern before using it in code.
Do I need to include slashes around my regex?
No. In this tool, enter the pattern only. For example, use \d+ instead of /\d+/g. Choose flags using the checkboxes.
What does the global flag do?
The global flag finds all matches in the text. Without it, JavaScript usually stops after the first match.
Why is my regex showing an error?
A regex error usually means the pattern has invalid syntax, such as an unclosed bracket, unclosed group or incorrect escape sequence.
Can I test regex replacement?
Yes. Enter replacement text in the replace preview section and click Preview Replace. Capture group replacements like $1 and $2 are supported.
Does this tool upload my text?
No. This Regex Tester runs in your browser using JavaScript. Your pattern and test text are not uploaded to TechFixRadar.
Is this Regex Tester free?
Yes. It is free to use with no signup, no download and no usage limit.