# Free A/B testing and CRO tools

Free, no-signup tools for planning experiments, checking significance, and preparing assets. Every tool runs in the browser.

- [A/B Testing Sample Size Calculator](https://www.otterab.com/free-tools/sample-size-calculator): Calculate the sample size each A/B test variant needs from your baseline conversion rate, minimum detectable effect, confidence level, and statistical power.
- [A/B Test Duration Calculator](https://www.otterab.com/free-tools/duration-calculator): Estimate how many days an A/B test should run using daily traffic, variant count, baseline conversion rate, detectable lift, and required sample size.
- [A/B Test Significance Calculator](https://www.otterab.com/free-tools/significance-calculator): Check A/B test statistical significance, conversion-rate lift, confidence, and whether your visitor and conversion counts support a winner.
- [A/B Test Hypothesis Generator](https://www.otterab.com/free-tools/hypothesis-generator): Turn an experiment idea into a clear A/B test hypothesis with an audience, proposed change, expected outcome, rationale, primary metric, and success criteria.
- [Design to A/B Test Hypothesis Generator](https://www.otterab.com/free-tools/design-hypothesis-generator): Compare control and variant designs, then generate an A/B test hypothesis with the proposed change, outcome, rationale, metric, and risk checks.
- [A/B Test Headline Generator](https://www.otterab.com/free-tools/headline-generator): Generate A/B test headline variants from your product, audience, core benefit, proof point, and tone, then copy the best ideas into your experiment brief.
- [Free Image Compressor for Websites](https://www.otterab.com/free-tools/free-image-compressor): Compress JPEG, PNG, and WebP images in your browser, resize large website assets, and export smaller product or landing-page images without uploads.
- [Shopify Image Compressor](https://www.otterab.com/free-tools/shopify-image-compressor): Compress and resize Shopify product, collection, hero, and banner images locally, then export smaller web-ready assets before uploading them to your store.
- [Ecommerce Image Optimizer](https://www.otterab.com/free-tools/ecommerce-image-optimizer): Optimize ecommerce product, collection, category, and campaign images with private browser-local compression, resizing, and WebP conversion before upload.
- [Product Image Compressor](https://www.otterab.com/free-tools/product-image-compressor): Shrink and resize product photos for ecommerce pages, online marketplaces, email, and paid ads entirely in your browser, without uploading customer assets.
- [Free WebP Image Converter](https://www.otterab.com/free-tools/webp-image-converter): Convert JPEG and PNG files to smaller WebP images in your browser, adjust quality and dimensions, and download web-ready files without an upload.
- [Amazon Image Compressor](https://www.otterab.com/free-tools/amazon-image-compressor): Resize and compress Amazon listing, lifestyle, A+ Content, storefront, and advertising images in your browser before uploading them to Seller Central.
- [Free FOMO Popup Generator](https://www.otterab.com/free-tools/fomo-popup-generator): Create installable social-proof and FOMO popup code for ecommerce campaigns with custom messages, placement, timing, colors, frequency, and a live preview.
- [Website Announcement Bar Generator](https://www.otterab.com/free-tools/announcement-bar-generator): Build a website announcement bar with custom copy, colors, CTA link, fixed positioning, optional close button, live preview, and installable JavaScript code.
- [A/B Test Result Image Generator](https://www.otterab.com/free-tools/ab-test-result-image-generator): Combine control and variant screenshots into a polished, shareable A/B test result image with labels, lift, confidence, winner status, and export controls.
- [Dynamic UTM Tracking Templates](https://www.otterab.com/free-tools/utm-template-generator): Copy dynamic UTM templates for Google Ads, Meta, TikTok, Pinterest, and Microsoft Advertising with macros for consistent campaign reporting.
- [Ecommerce CRO Checklist](https://www.otterab.com/free-tools/ecommerce-cro-checklist): Audit your store with a 100-point ecommerce CRO checklist covering navigation, product pages, trust, carts, checkout, mobile UX, and analytics.
- [Ecommerce A/B Test Playbook](https://www.otterab.com/free-tools/ecommerce-ab-test-playbook): Browse practical ecommerce A/B test ideas for home, collection, product, cart, and checkout pages, then filter the playbook by impact and implementation effort.
- [Minimum Detectable Effect Calculator](https://www.otterab.com/free-tools/mde-calculator): Calculate minimum detectable effect from baseline and target conversion rates, compare absolute and relative lift, and plan a realistic A/B test.
- [Conversion Rate Calculator](https://www.otterab.com/free-tools/conversion-rate-calculator): Calculate website conversion rate from visitors and conversions, compare it with a target, and estimate traffic needed for a chosen conversion count.
- [Sample Ratio Mismatch Checker](https://www.otterab.com/free-tools/sample-ratio-mismatch-checker): Check an A/B test for sample ratio mismatch by comparing observed allocation with the intended split and calculating a chi-square probability.
- [A/B Test Revenue Impact Calculator](https://www.otterab.com/free-tools/revenue-impact-calculator): Estimate monthly A/B test revenue impact from traffic, conversion rate, average order value, and expected lift, including incremental revenue.
- [A/B Test Prioritization Calculator](https://www.otterab.com/free-tools/test-prioritization-calculator): Prioritize A/B test ideas by impact, confidence, ease, reach, and learning value so the strongest experiments move into your roadmap first.

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