Which regex engine is used?

The tester uses the browser JavaScript RegExp engine, so behavior matches modern web applications.

Why does a valid-looking regex fail?

JavaScript needs escaped backslashes and supports a specific flag set. Check the error panel for syntax details.

Can this generate a final production regex?

Use generated or preset patterns as a draft, then test positive and negative samples in the JavaScript runtime that will use the pattern.

Why are capture groups important before copying?

Capture groups decide which part of the matched text your code receives, so inspect group output before using a pattern in parsing, routing, or validation.

Regex Tester - Free Online JavaScript Regex Tool

regex testerregular expression testerjavascript regexregex cheat sheetPrivacy: Browser local

Regex Tester

Test JavaScript regular expressions, inspect matches, and keep common patterns close by.

Input / Output

Start with the tool

Input, output, and copy actions stay in this main surface. Examples and reference checks are separated below.

Copy-ready output

PatternFlags

Pattern presets

Regex snippets

Apply common production patterns, then verify them against your own sample before copying.

Find common email addresses in logs, forms, and pasted payloads.

\b[A-Z0-9._%+-]+@[A-Z0-9.-]+\.[A-Z]{2,}\b

URL

Extract http and https URLs without swallowing quotes, angle brackets, or trailing sentence punctuation.

https?:\/\/[^\s"'<>]*[A-Za-z0-9/#]

ISO date

Match yyyy-mm-dd dates before validating calendar rules in code.

\b\d{4}-\d{2}-\d{2}\b

UUID v4

Find UUID values in request IDs, fixtures, and copied API responses.

\b[0-9a-f]{8}-[0-9a-f]{4}-[1-5][0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}\b

IPv4

Spot IPv4 addresses in server logs and DNS troubleshooting notes.

\b(?:25[0-5]|2[0-4]\d|1?\d?\d)(?:\.(?:25[0-5]|2[0-4]\d|1?\d?\d)){3}\b

Hex color

Collect CSS hex colors including short, six-digit, and alpha forms.

#(?:[0-9a-fA-F]{3}|[0-9a-fA-F]{6}|[0-9a-fA-F]{8})\b

Slug

Match lowercase URL slugs used in routes, docs, and content IDs.

\b[a-z0-9]+(?:-[a-z0-9]+)*\b

Sample text

Matches

Effective flags

Match details

Inspect positions and capture groups before copying the pattern.

#1 @ 15

2026-06-05

Group 1: 2026Group 2: 06Group 3: 05

#2 @ 30

2026-07-01

Group 1: 2026Group 2: 07Group 3: 01

Related tools

Useful next steps

Next step:

URLNext step: Encode values before nesting them inside query strings.DiffNext step: Paste two versions to see added and removed lines or words.JSONNext step: Format compact API responses before copying them into code or docs

Output

Raw match JSON

Copy-ready output

[
  {
    "index": 1,
    "text": "2026-06-05",
    "position": 15,
    "groups": [
      "2026",
      "06",
      "05"
    ]
  },
  {
    "index": 2,
    "text": "2026-07-01",
    "position": 30,
    "groups": [
      "2026",
      "07",
      "01"
    ]
  }
]

Generate from examples

Draft a starting pattern from positive and negative examples, then test it above before copying.

Positive examplesNegative examples

Confidence

92%

Positive matches

Negative matches

Suggested pattern

\b\d{4}-\d{2}-\d{2}\b

Generator warnings

Generated pattern is ready for review in the tester above.

Local session

Input state is saved only in this browser so you can restore the last workspace without an account.

Review after the result

Open examples, checks, and related tools only after the primary input/output flow is done.

Guides

Examples

Starting points for this utility

^[^\s@]+@[^\s@]+\.[^\s@]+$https?:\/\/[^\s"'<>]*[A-Za-z0-9/#]\b(?:25[0-5]|2[0-4]\d|1?\d?\d)(?:\.(?:25[0-5]|2[0-4]\d|1?\d?\d)){3}\b

Use cases

Code

Validate JavaScript regular expressions
Inspect capture groups and match positions

Run one positive sample and one negative sample before copying the pattern.
Confirm each flag is intentional: g, i, m, s, u, or y.
Copy either the raw pattern or the slash-wrapped form based on the target API.