Build the regex. See every match. Save it for next time.
Live highlight, capture-group inspector, plain-English explanations, and a curated library of the patterns you keep re-inventing.
Plans from $5/mo — cancel any time
Stop pasting regex into Stack Overflow
Test, explain, save — without leaving the page or losing your work.
Live match highlighting
Type a regex, type a test string — every match lights up instantly. Capture groups shown inline with named-group support.
Plain-English explainer
Paste any regex, get a step-by-step explanation: lookbehind, anchors, character classes, quantifiers, flags. Every piece described in normal English.
Pattern library
Email, URL, IPv4, IPv6, UUID, ISO-8601, phone, credit card, slug, hex color — curated patterns that pass real edge cases (not the 5-line Stack Overflow ones).
Save your own
Every regex you write — name it, tag it, come back to it. Pro accounts cloud-sync across devices.
Replace mode
Test substitutions with backreferences ($1, $2). See exactly what your sed / JS .replace() call would produce.
Multi-flavor
Switch between JavaScript, PCRE and POSIX flavors. RegexBuilder tells you which features are supported in each.
Three steps
From a fuzzy idea to a tested, explained regex.
Pick or paste
Start from a library pattern or paste a regex you've already written.
Test
Live-highlight matches on any test string. Edit until it does what you want.
Save
Name, tag, copy to clipboard, paste into your code.
Simple pricing
Pick a plan and stop re-inventing regex.
For solo devs
- 200 saved patterns / mo
- Plain-English explainer
- Full pattern library
- Replace mode
For data + security teams
- 5000 saved patterns / mo
- Multi-flavor (JS / PCRE / POSIX)
- Cloud sync across devices
- Team-shared library
- Priority support
Frequently asked
Which regex flavors do you support?
JavaScript (default), PCRE-compatible, and POSIX. We mark unsupported features clearly when you switch flavors.
Does my test string leave my browser?
No. Everything is client-side; we don't send your regex or test strings to a server unless you opt in to cloud-sync your saved patterns.
Can it explain a regex I didn't write?
Yes — that's exactly what the explainer does. Paste any regex and get a step-by-step plain-English breakdown.
Do I get a free trial?
No — this is a paid tool with plans from $5 a month. Starter is $5/mo and Pro is $15/mo; you can cancel any time.
How do I cancel?
From your account page, or by emailing us. Cancellation stops the next renewal.
Regex answers
The pattern, what every part of it does, and inputs it accepts and rejects — each one run through the engine, not copied from somewhere else.
- Regex for an email address
- Regex for a US phone number
- Regex for an IPv4 address
- Regex for a URL
- Regex for a date in YYYY-MM-DD format
- Regex to match digits only
- Regex for alphanumeric characters
- Regex to find special characters
- Regex for a strong password
- Regex to match whitespace
- Regex to trim leading and trailing whitespace
- Regex for a UUID
- Regex for a hex colour code
- Regex for a US ZIP code
- Regex for a UK postcode
- Regex for a credit card number
- Regex for a domain name
- Regex to extract a file extension
- Regex to match an HTML tag
- Regex for a decimal number
- Regex for a negative number
- Regex to match empty lines
- Regex to find duplicate consecutive words
- Regex for a Base64 string
- Regex for a URL slug
- Regex for a semantic version
- Regex for a 24-hour time
- Regex for a MAC address
- Regex for an IPv6 address
- Regex for a dollar amount
- Regex for a non-greedy match
- Regex for a line that does not contain a word
- Regex with a named capture group
- Regex lookahead explained
- Regex multiline flag explained
- Regex to match letters in any language
- Regex word boundary explained
- Regex to find a repeated character
- Regex to split a comma-separated list
- Regex to capitalise the first letter