Regex Tester Online
Test regular expressions against your text instantly. Find matches, inspect capture groups, highlight results, and troubleshoot regex patterns directly in your browser.
Choosing an example replaces the pattern, flags, and test string.
Enter the raw pattern without surrounding slashes — flags are configured separately below.
What Is a Regex Tester?
A Regex Tester Online is a tool for checking how a regular expression matches text. Enter a pattern, add sample text, and inspect the matching portions of the input. A regex tester can help you troubleshoot patterns, verify validation rules, examine capture groups, and test find-and-replace behavior without repeatedly writing temporary code.
A regular expression, also called a regex or regexp, is a sequence of characters that describes a text pattern. Developers use regular expressions to find, validate, extract, split, or replace text in applications, documents, logs, and data files.
Jomatter's online regex tester is designed to make pattern testing easier with a pattern field, test text, match results, and controls for supported regular expression flags. It helps developers, testers, students, and analysts check a pattern against real examples before using it in a project.
Example Regex Pattern
Example Test Text
The example pattern matches common email-like strings with a local part, an at sign, a domain, and a suffix of at least two letters. It is useful for demonstrating regex matching, but it is not a complete check of every valid email address.
Remember: A regex match only tells you whether text fits the pattern you wrote. It does not automatically prove that an email address, phone number, URL, or other value exists or is valid in every real-world context.
How to Test Regex Online
Follow these steps to check a regular expression against sample text and understand its results.
Type the regular expression into the pattern field. Start with a small pattern and add more conditions as needed.
Paste or type the text you want to check. Include both examples that should match and examples that should not match.
Enable supported options such as global, case-insensitive, or multiline matching when the pattern requires them.
Review highlighted matches and captured values to see which parts of the input matched the expression.
Enter a replacement string when replacement testing is available. References such as 1,2, and $& can reuse captured text or the full match.
Adjust the expression, retest edge cases, and copy the verified pattern into the code or tool where you need it.
Test more than one sample before relying on a regex. Include empty input, unexpected punctuation, different letter cases, line breaks, and boundary values relevant to your application.
Key Features of an Online Regex Tester
A regular expression tester brings pattern editing and test results together so you can develop and troubleshoot expressions more efficiently.
Real-Time Regex Matching
Check how a pattern matches your sample text as you edit the expression or input, where live updates are supported.
Match Highlighting
Identify matching text in the input and see which parts of a string are selected by the expression.
Capture Group Inspection
Examine numbered capture groups and, for supported patterns, named groups to understand which text each group captures.
Regex Flag Controls
Change matching behavior with supported flags such as g, i, m, s, u, and y.
Find and Replace Testing
Test how matched text is replaced, including the use of capture references in replacement strings.
Match Positions and Results
Use match details, positions, and captured values where available to investigate unexpected results and improve a pattern.
ECMAScript Regex Support
Test expressions using JavaScript regular expression behavior, suitable for patterns intended for modern browsers and Node.js.
Browser-Based Access
Open the tool in a modern browser and test patterns without installing a separate desktop application.
Regex flavor matters: Regular expression syntax differs across programming languages. A pattern that works in JavaScript may need changes for Python, PCRE, Java, Go, or .NET. Check the regex engine used by your target application before reusing a pattern.
Regex Flags Explained
Regex flags modify how an expression searches text. The following flags are commonly used with JavaScript regular expressions.
| Flag | Name | What it does | Typical use |
|---|---|---|---|
g |
Global | Finds multiple matches instead of stopping after the first match during a global search. | Extracting every occurrence from a string. |
i |
Case-insensitive | Matches letters without distinguishing uppercase from lowercase in the usual case-sensitive way. | Finding a word regardless of capitalization. |
m |
Multiline | Changes the behavior of ^ and $ so they can match line boundaries as well as string boundaries. |
Checking each line in a log or text block. |
s |
DotAll | Allows . to match line terminator characters too. |
Matching text that spans multiple lines. |
u |
Unicode | Enables Unicode-aware matching behavior and escape handling. | Working with Unicode text and code-point escapes. |
y |
Sticky | Requires a match to start at the position indicated by the expression's lastIndex state. |
Matching sequential tokens at an exact position. |
Use only the flags your pattern needs. The global and sticky flags also affect how JavaScript regular expression methods track matching positions, so repeated tests should account for the engine's state behavior.
Common Regex Examples
These examples demonstrate common text-matching tasks. Some patterns check format only; they do not guarantee that a value is valid according to every application or real-world rule.
| Use case | Regex pattern | What it checks |
|---|---|---|
| Email-like format | ^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$ |
A common email address shape with a domain suffix. |
| URL-like text | https?:\/\/[^\s]+ |
Text beginning with HTTP or HTTPS followed by non-whitespace characters. |
| Phone-like value | ^\+?[0-9\s\-()]{7,20}$ |
A loose phone format using digits, spaces, parentheses, hyphens, and an optional leading plus. |
| Date format | ^\d{4}-\d{2}-\d{2}$ |
A string shaped like YYYY-MM-DD; it does not check calendar validity. |
| Alphanumeric only | ^[a-zA-Z0-9]+$ |
One or more ASCII letters or digits, with no other characters. |
| Password pattern | ^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[^\w\s]).{8,}$ |
At least eight characters, including a lowercase letter, uppercase letter, digit, and non-word, non-whitespace character. |
| Tag-like text | <[^>]+> |
Text surrounded by angle brackets; it is not a full HTML parser. |
| Whitespace | \s+ |
One or more whitespace characters. |
Testing tip: Try expected matches and non-matches for every example. For strict email, URL, phone, date, or password validation, combine pattern testing with the application's actual validation requirements.
Regex Cheat Sheet
Use this quick reference to understand common regex symbols and grouping syntax when writing or debugging a pattern.
| Symbol | Meaning | Example or note |
|---|---|---|
. |
Any character except line terminators by default. | The s flag changes this behavior. |
* |
Zero or more repetitions. | ab* matches a, ab, or abb. |
+ |
One or more repetitions. | \d+ matches one or more digits. |
? |
Zero or one repetition; also used in other regex constructs. | colou?r matches colour and color. |
^ |
Start of input, or start of line with multiline mode. | ^Hello |
$ |
End of input, or end of line with multiline mode. | end$ |
\d |
A digit character in JavaScript regex. | \d{4} matches four digits. |
\w |
A word character, generally ASCII letters, digits, or underscore in JavaScript. | \w+ |
\s |
A whitespace character. | \s+ |
[abc] |
Any one character from the listed set. | Matches a, b, or c. |
[^abc] |
Any character not in the listed set. | Inside a character class, a leading caret negates the set. |
(...) |
Capturing group. | Stores a matched portion for later reference. |
(?:...) |
Non-capturing group. | Groups parts without creating a capture. |
(?<name>...) |
Named capture group. | Assigns a name to a captured value in supported engines. |
{2,5} |
Between two and five repetitions. | Applies to the preceding character or group. |
| |
Alternation, meaning OR. | cat|dog matches either word. |
Who Uses a Regex Tester?
A regular expression tester is useful whenever a task involves finding patterns in text, validating input, extracting values, or replacing selected content.
Web Developers
Test input validation rules, search patterns, and text-processing logic before adding them to a web application.
Backend Developers
Extract values from logs, process text fields, and test patterns used in APIs and application workflows.
QA Engineers
Check validation behavior with valid, invalid, and edge-case inputs as part of a testing process.
Data Analysts
Find structured values in text exports and prepare data for cleanup or transformation.
SEO Specialists
Test patterns for URL matching, redirect rules, and text searches while accounting for the requirements of the system being used.
Students and Administrators
Learn regex syntax or search server logs, configuration text, and other large text collections.
Regex Testing Tips
Regular expressions can become difficult to maintain when many conditions are combined. These habits can make patterns easier to understand and safer to use.
- Start small: Begin with the simplest pattern that matches your requirement, then add conditions one at a time.
- Test edge cases: Include empty strings, punctuation, line breaks, different letter cases, and values near length limits.
- Use capture groups deliberately: Use
(...)to capture needed text and(?:...)when you only need grouping. - Enable global matching when needed: Use the
gflag when you want multiple matches rather than only the first match. - Escape special characters: Escape characters such as
.,+,?,(,),[,],{,},|,^,$, and\when you need their literal meaning. - Watch greedy quantifiers: Quantifiers such as
.*may consume more text than expected. Consider whether a more specific character class or a lazy quantifier is appropriate. - Match the target engine: Syntax and features vary between JavaScript, Python, PCRE, Java, Go, and .NET.
- Consider performance: Avoid unnecessarily complex patterns and test them against long or adversarial inputs, especially in applications that process user-supplied text.
Safety note: Some poorly designed patterns can take a very long time to process certain inputs because of excessive backtracking. Use reasonable input limits and evaluate performance before using complex regex patterns on untrusted text.
Is My Regex Test Data Private?
Jomatter's Regex Tester is designed to perform regex matching in your browser. Under this client-side approach, the pattern and test text used for matching do not need to be sent to a remote formatting or testing service.
Browser-based testing can be useful when inspecting sample logs, configuration text, or private development data. However, review the page and your environment before entering highly sensitive information. Avoid pasting production secrets, passwords, access tokens, or private customer data into tools unless you have confirmed that the workflow is suitable for that information.
Security tip: Local regex testing does not encrypt your input or remove sensitive information. Check what you paste, copy, and share, and use safe test data whenever possible.
Frequently Asked Questions
What is a regex tester?
A regex tester is a tool that lets you enter a regular expression and sample text to see whether the pattern matches and which portions of the text are selected.
Is this regex tester free?
Jomatter's Regex Tester is intended for free online use without requiring a separate desktop installation. Any access limits depend on the tool as deployed on the page.
Which regex flavor does this tool use?
This tester uses JavaScript regular expression behavior, also known as ECMAScript regex. Patterns intended for other languages may need adjustments because regex features and syntax differ between engines.
Can I test capture groups?
Capture groups let you isolate parts of a match. The numbered groups and named groups supported by the pattern can be inspected when the tool exposes capture details.
Can I test regex replacement?
When replacement testing is available, enter a replacement string to see how matched text changes. JavaScript replacement strings can use references such as 1,2, and $& for captured groups and the full match.
What does the global flag do?
The g flag enables global matching, so a search can return multiple matches instead of stopping after the first. The exact result also depends on the JavaScript method used.
Why does my regex not match?
Check whether the pattern has the right anchors, character classes, escaping, case sensitivity, and flags. Confirm that the test text contains the expected characters and that the pattern is written for the correct regex engine.
Is my test data private?
The tool is designed to process regular expressions locally in your browser. Avoid entering secrets or sensitive personal data unless you have verified that your environment and workflow are appropriate.
Can I use the regex tester on mobile?
You can open the tool in a modern mobile browser. The editing experience may vary depending on screen size, browser features, and the complexity of the pattern.
Can one regex work in every programming language?
No. Regex syntax and supported features differ among engines. Test the expression in the same language or runtime that will use it, particularly when using lookbehind, named groups, Unicode features, or engine-specific syntax.
Does a regex guarantee valid input?
No. A regex checks whether text matches a particular pattern. A match does not necessarily confirm that the value exists, is reachable, or meets every business or domain-specific rule.
What is the difference between a regex tester and a regex generator?
A regex tester checks a pattern against sample text. A regex generator helps build a pattern from a description or selected requirements. A tester is useful for verifying the generated result before using it in code.