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 — RegexBuilder is a paid tool from $5/mo. The library and demo on the landing page show what you get.
How do I cancel?
From your account page, or by emailing us. Cancellation stops the next renewal.