Field guides for people who run experiments, not opinions.
A beginner-grade growth-fundamentals series, long-form field guides on digital marketing, a picker for founder experiment strategy, a vocabulary glossary for the language of experiments, honest comparisons against the experimentation tools you already use, and interactive calculators that do the math for you.
Growth fundamentals, for total beginners
Seven short lessons for people who have never done marketing or growth before. What it is, who your customer is, the four ways products grow, and why experimentation matters. Read first, then move to the field guide.
Start with the basicsDigital marketing, end to end
Channels, analytics, buyer psychology, SEO, email, paid, social, GTM, conversion optimization, and the marketing layer for product managers, written as a system, not a menu.
Browse the seriesFounder experiment picker
Turn messy founder questions about demand, channels, pricing, positioning, activation, retention, sales, ICP, and AI operators into one measurable experiment contract.
Open the pickerThe vocabulary of marketing experiments
Plain definitions for experiment OS, kill threshold, hypothesis floor, verdict, contract, and the rest of the vocabulary Xi runs on.
Open the glossaryXi vs. the experimentation tools
Side-by-side breakdowns against Optimizely, Statsig, and VWO. Each one shows where the other tool is the right call, and where Xi is.
See the comparisonsThe math, made interactive
An A/B test sample-size calculator. Plug in your baseline, the lift you want to detect, and your monthly traffic — get the verdict in plain English.
Open the calculatorPick the experiment that fits your traffic
Most founders default to A/B tests because they’re loudest. Tell us your stage, your goal, and your traffic — get the experiment shape that actually concludes.
Open the pickerScore your hypothesis in 10 seconds
Paste a hypothesis. Get a 0-100 rigor score, six dimension checks, an improved rewrite, and a suggested kill threshold. No login, no credit card.
Score a hypothesis