Free Regex Tester Online — Live Match, Groups & Replace
Last Updated: May 2026 · 6 min read
Regular expressions are one of the most powerful tools in a developer's toolkit — and one of the most frustrating to write blind. Our free online regex tester gives you a live environment to write, test, and refine regex patterns with instant match highlighting, capture group inspection, and replace preview. No signup. No installs.
What Is a Regular Expression?
A regular expression (regex or regexp) is a sequence of characters that defines a search pattern. They're used in virtually every programming language for:
- Validation: email addresses, phone numbers, URLs, passwords
- Parsing: extracting data from logs, HTML, CSV, or API responses
- Search & replace: bulk text transformations in code editors, scripts, or databases
- Routing: URL pattern matching in web frameworks (Express, Django, FastAPI, Rails)
Basic Regex Syntax Reference
| Pattern | Meaning | Example |
|---|---|---|
. |
Any character except newline | a.c matches abc, a1c |
* |
0 or more of previous | ab*c matches ac, abc, abbc |
+ |
1 or more of previous | ab+c matches abc, abbc |
? |
0 or 1 of previous (optional) | colou?r matches color, colour |
^ |
Start of string | ^Hello matches only strings starting with Hello |
$ |
End of string | world$ matches only strings ending with world |
\d |
Any digit (0–9) | \d{4} matches 2026 |
\w |
Word character (a-z, A-Z, 0-9, _) | \w+ matches words |
\s |
Whitespace (space, tab, newline) | \s+ matches gaps |
[abc] |
Character class | [aeiou] matches any vowel |
[^abc] |
Negated class | [^aeiou] matches non-vowels |
(abc) |
Capture group | (foo)(bar) captures two groups |
(?:abc) |
Non-capturing group | Groups without capturing |
a\|b |
Alternation (OR) | cat\|dog matches either |
{n} |
Exactly n times | \d{3} matches exactly 3 digits |
{n,m} |
Between n and m times | \d{2,4} matches 2–4 digits |
Regex Flags Explained
| Flag | Meaning |
|---|---|
g |
Global — find all matches, not just the first |
i |
Case-insensitive — A matches a |
m |
Multiline — ^ and $ match start/end of each line |
s |
Dotall — . also matches newline characters |
Practical Regex Examples
Email validation
^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$
URL extraction
https?:\/\/[^\s"'<>]+
Phone number (US)
\+?1?\s*\(?\d{3}\)?[\s.-]\d{3}[\s.-]\d{4}
IPv4 address
\b(?:(?:25[0-5]|2[0-4]\d|[01]?\d\d?)\.){3}(?:25[0-5]|2[0-4]\d|[01]?\d\d?)\b
ISO date (YYYY-MM-DD)
\d{4}-(0[1-9]|1[0-2])-(0[1-9]|[12]\d|3[01])
Extract JSON keys
"([^"]+)":\s*
HTML tag stripping
<[^>]+>
Password strength (8+ chars, upper, lower, digit, special)
^(?=.*[a-z])(?=.*[A-Z])(?=.*\d)(?=.*[@$!%*?&])[A-Za-z\d@$!%*?&]{8,}$
Capture Groups and Back-References
Capture groups are wrapped in () and allow you to extract specific parts of a match or reference them in replacements.
Example: Extract year, month, day from a date string
Pattern: (\d{4})-(\d{2})-(\d{2})
Input: 2026-05-18
Group 1: 2026
Group 2: 05
Group 3: 18
Replace with back-references:
Pattern: (\d{4})-(\d{2})-(\d{2})
Replace: $3/$2/$1
Result: 18/05/2026
Our free regex tester shows all capture groups in a table and supports $1, $2... back-references in the replace field.
How to Use the Free Regex Tester
- Go to SolutionGigs Free Regex Tester
- Enter your regex pattern (without slashes)
- Select flags:
g(global),i(case-insensitive),m(multiline),s(dotall) - Paste your test string in the text area
- Match tab: see all matches highlighted in real time
- Replace tab: enter a replacement string (supports
$1,$2groups) - Groups tab: see every capture group for every match in a table
- Click any example chip to load a pre-built pattern
All processing is instant and runs in your browser — no server calls, completely free.
Regex in Different Languages
The same core syntax works across languages, but there are subtle differences:
| Language | Flavor | Notes |
|---|---|---|
| JavaScript | ECMA | No lookbehind in older engines; RegExp object |
| Python | re module |
(?P<name>...) for named groups |
| Java | java.util.regex |
Verbose but powerful; Pattern + Matcher |
| PHP | PCRE | Use preg_match, preg_replace |
| Ruby | Oniguruma | Similar to PCRE; =~ operator |
| Go | RE2 | No lookahead/lookbehind; designed for linear time |
| .NET | .NET regex | Rich feature set including balancing groups |
Our regex tester uses JavaScript's built-in regex engine — perfect for front-end, Node.js, and general regex learning.
Try the Free Regex Tester
SolutionGigs Free Regex Tester — write, test, and refine patterns with live highlighting. No signup, 100% free.
Frequently Asked Questions
What is a regular expression? A regular expression (regex) is a sequence of characters defining a search pattern. Used in programming to find, validate, or replace text. For example, \d{3}-\d{4} matches a phone number pattern like 555-1234.
What does .* mean in regex? The dot (.) matches any single character except newline. The asterisk () means zero or more of the preceding element. So . matches any sequence of characters (including empty strings). Use .+ to require at least one character.
What is the difference between greedy and lazy matching? Greedy matching (default) consumes as many characters as possible. Lazy matching (add ? after the quantifier, like .*?) consumes as few as possible. For example, <.+> greedily matches a whole HTML string; <.+?> lazily matches each individual tag.
How do I test a regex for an email address? A basic email regex: ^[\w.-]+@[\w.-]+.[a-zA-Z]{2,}$ — matches most standard email formats. Paste it into our regex tester with sample emails to see exactly what matches and what doesn't in real time.
Is the regex tester free? Yes — completely free, no account needed. Enter your pattern and test string, see live highlighted matches, capture groups, and the replace preview. Supports JavaScript regex syntax with all flags (g, i, m, s).
Mohammed Yaseen
Founder, SolutionGigs
Mohammed has been building developer tools since 2018 and writes about JSON, JWT, regex, SQL, APIs, and web development utilities. LinkedIn →