Regex Cheatsheet Builder
Build a printable regex cheatsheet filtered to your flavor — JavaScript, PCRE or Python — and only the feature groups you use.
About this tool
Regex Cheatsheet Builder
Build a printable regex cheatsheet filtered to your flavor — JavaScript, PCRE or Python — and only the feature groups you use.
The Regex Cheatsheet Builder generates a reference sheet of regular-expression tokens filtered to a single flavor — JavaScript (ECMA-262), PCRE2 or Python's re module — so every token shown is one your engine actually supports. Developers pick the feature groups they use (anchors, classes, quantifiers, groups, lookaround, flags, escapes) and get a copyable Markdown or printable sheet with per-token examples and cross-flavor notes.
How to use Regex Cheatsheet Builder
- 1
Open Regex Cheatsheet Builder on AltFTool — it loads instantly in your browser.
- 2
Paste your code or data sample into the workspace.
- 3
Pick the format, conversion, or analysis you need.
- 4
Copy the polished result straight back into your project.
Why use Regex Cheatsheet Builder
Flavor-accurate
Tokens unsupported by your engine are hidden entirely, so nothing on the sheet fails when pasted.
Only what you use
Toggle seven feature groups on or off to keep the sheet short enough to actually scan.
Markdown export
One click copies the whole sheet as GitHub-flavored Markdown tables for wikis and READMEs.
Common use cases
- Generate a JavaScript-only cheatsheet before a code review so nobody pastes PCRE-only syntax like \A or possessive quantifiers into a Node.js validator.
- Print a Python re reference for a data-cleaning sprint that shows (?P<name>...) group syntax instead of the (?<name>...) form Python rejects.
- Copy a Markdown cheatsheet of just lookaround and groups into your team wiki when onboarding developers to an existing log-parsing codebase.
Frequently asked questions
What is the difference between JavaScript, PCRE and Python regex?
The core syntax is shared, but each flavor has exclusive features: JavaScript has the g, y and u flags but no \A or \z anchors; PCRE2 adds possessive quantifiers, atomic groups and \x{...} code points; Python uses (?P<name>...) for named groups and re.VERBOSE for extended mode. This builder tracks those differences per token so the sheet only shows what your engine accepts.
Does JavaScript regex support lookbehind?
Yes — both positive (?<=...) and negative (?<!...) lookbehind have been part of JavaScript since ES2018 and work in all current browsers and Node.js. Python also supports lookbehind but requires it to be fixed-width, which the sheet notes on the token.
Why is \A not working in my JavaScript regex?
JavaScript has no \A or \z anchors at all — in a regex literal \A just matches the letter A. Use ^ and $ without the m flag to anchor to the start and end of the whole string; \A and \z (or \Z in Python) exist only in flavors like PCRE and Python.
Do possessive quantifiers like \d++ work in Python?
Only from Python 3.11 onward — earlier versions raise a re.error for possessive quantifiers and atomic groups. In JavaScript they are not supported in any version; the usual workaround is a plain greedy quantifier or restructuring the pattern to avoid catastrophic backtracking.