Optimizely

Optimizely is an experimentation platform. You change part of a page, such as a headline, a product page layout or a checkout step, show the new version to a share of visitors and measure whether it changes conversion. It handles splitting the traffic, keeping each visitor in the same version and running the statistics.

It is built for teams that run many tests at once, with developers who can set up server-side experiments as well as visual ones. The wider product line also covers content management and commerce.

For a smaller store, the question is traffic. A test needs enough orders in each version to reach a clear result, and low-traffic shops can wait weeks for an answer. Check the minimum traffic your plan assumes before committing.