What free tools does Otter offer?

A whole toolbox of free helpers for running better tests, all at otterab.com/free-tools. They fall into a few groups: calculators (work out how big or long a test needs to be, and whether a result is real), idea generators (turn a rough idea into a proper test plan or headline), image tools (shrink images so your pages load faster), and written guides (checklists and playbooks). Pick whatever helps.

Do I need an account to use them?

No. The free tools are open to everyone — no sign-up, no login, no cost. Just open the page and use it. They're handy whether you're a customer or just getting started with testing.

Which calculators are there?

The planning ones: a Sample Size Calculator (how many visitors you need), a Duration Calculator (how long that takes at your traffic), a Minimum Detectable Effect calculator (the smallest change worth chasing), and a Test Prioritization calculator (which idea to run first). The checking ones: a Significance Calculator (is this result real?), a Conversion Rate Calculator, a Revenue Impact Calculator, and a Sample Ratio Mismatch Checker (is your traffic split healthy?).

What about the generators?

These help you go from a blank page to a plan: a Hypothesis Generator and a Design-to-Hypothesis Generator turn an idea (or a screenshot) into a clear, testable statement; a Headline Generator gives you variations to test; and there are quick builders for things like FOMO popups, announcement bars, and UTM link templates.

Are there tools for images and page speed?

Yes. There are free image compressors — general, plus ones tuned for Shopify, ecommerce, product photos, and Amazon — and a WebP converter. Smaller images mean faster pages, and faster pages usually convert better, so they pair nicely with testing.

Where do I find all of them?

Everything lives on the Free Tools page at otterab.com/free-tools, where each tool has its own page with simple instructions. There are also written resources there, like an Ecommerce CRO Checklist and an A/B Test Playbook, if you'd rather read than calculate.

Getting Started3 min read

Free Tools

A free set of calculators, generators, and guides for planning and checking tests — no account required.

Browse docs

A free toolbox for planning and checking tests — calculators, idea generators, image compressors, and guides. No account needed, no cost.

Alongside the main app, Otter publishes a set of free tools anyone can use — no sign-up, no login. They're handy for planning a test before you build it, sanity-checking a result, or speeding up your pages. For a frequentist manual split, the sample-size and significance calculators use the same formulas as the wizard and results page. Bayesian manual splits and bandits rely on live decision reporting instead of a fixed sample target.

Calculators

Plan and check a frequentist manual split with the same formulas as the dashboard.

Sample Size · Duration · Minimum Detectable Effect · Test Prioritization · Significance · Conversion Rate · Revenue Impact · Sample Ratio Mismatch Checker

Idea & content generators

Go from a blank page to a clear, testable plan.

Hypothesis Generator · Design-to-Hypothesis · Headline Generator · FOMO Popup · Announcement Bar · UTM Link Templates

Image & speed tools

Shrink images so your pages load faster (faster pages convert better).

Image Compressor · Shopify / Ecommerce / Product / Amazon compressors · WebP Converter

Guides

Read, don’t calculate — step-by-step playbooks and checklists.

Ecommerce CRO Checklist · A/B Test Playbook

Find them all on the Free Tools page, where each tool has its own page with simple instructions.

When to reach for a free tool

Before a frequentist manual split: use the Sample Size and Duration calculators to check it is worth running at your traffic — if it would take six months, pick a bigger change.

While planning the idea: the Hypothesis and Headline generators turn a hunch into something specific enough to test well.

Sanity-checking a manual split: the Significance and Sample Ratio Mismatch tools mirror the compatible checks in the results page and the Experiment health card — useful for a quick second opinion or for numbers from elsewhere.

Frequently asked questions

Quick answers to the questions teams ask most about this part of Otter.