A/B Testing

A/B testing lets you compare two (or more) variants of a template change on live traffic. The platform splits visitors into variants, the template renders differently per variant, and the results are evaluated in Google Analytics 4.

How it works:

1. You define variant codes in config.json.
2. On the first pageview, each visitor is randomly assigned one variant. The assignment is stored in the ab cookie for 30 days, so a visitor keeps seeing the same variant.
3. The template branches on the assigned variant.
4. Each pageview reports the variant to Google Analytics 4 (as an experience_impression event), where you compare conversion rates, revenue, or any other metric between variants.

Configuration

Define the test in config.json (see Configuration):

{
    "AB": {
        "variants": ["menu2026-a", "menu2026-b"]
    }
}

The variant codes are arbitrary strings (up to 64 characters) — they are what you will see in Google Analytics. Include an experiment identifier in the codes (menu2026-a, not just a) so that data from successive experiments never mixes together in analytics.

At least two unique variants are required. To end the test, remove the AB key from config.json.

Template Conditions

Branch on this.ABVersion in any template:

{% if this.ABVersion == 'menu2026-a' %}
    {% include "menu_variant_a.tpl" %}
{% elseif this.ABVersion == 'menu2026-b' %}
    {% include "menu_variant_b.tpl" %}
{% else %}
    {% include "menu_default.tpl" %}
{% endif %}

You must always provide a fallback branch (the final else) for the case where this.ABVersion is null or holds a code that is not one of yours. This happens for bots and crawlers (they are never assigned a variant, so they consistently see the fallback), for requests where the test is not active, and right after you remove the test from config.json, when visitors may briefly carry a cookie with a code from one of the platform's internal experiments.

Forcing a Variant

To preview a specific variant, append ?_forceAB=code to any URL, where code is the variant code:

https://www.example.com/?_forceAB=menu2026-b

This stores the chosen variant in your ab cookie, so it persists for your subsequent pageviews.

Evaluating in Google Analytics 4

If the shop has a Google Analytics 4 measuring code configured, every pageview with an assigned variant automatically sends the event Google defines for experiment integrations:

gtag("event", "experience_impression", {"exp_variant_string": "menu2026-b"});

To work with the variant in GA4 reports:

1. Register the dimension — in GA4: Admin → Custom definitions → Create custom dimension, with scope Event and event parameter exp_variant_string. Data collected before the registration stays available for audiences but not for Explorations.
2. Compare variants — in Explore, create segments filtered by the exp_variant_string dimension (one per variant) and compare conversions, revenue, or engagement between them. Standard reports support up to four comparisons at once.
3. Audiences (optional) — create one audience per variant (condition on exp_variant_string) to segment any standard report by test variant.

Use Admin → DebugView or the Realtime report to verify the event is coming in right after you deploy the test.

The assigned variant is also recorded outside GA4: it is stored with each order's traffic-source data and in the platform's own visit analytics (every pageview, visit, and conversion carries the variant), so order-level and visit-level analyses are possible on request even for traffic that ad blockers hide from GA4.

Things to Keep in Mind

• Sample size — an A/B test needs enough traffic to be meaningful. Before acting on a result, make sure both variants have enough sessions and that the measured change makes sense — otherwise you may effectively be measuring an A/A test.
• One test at a time — the platform supports a single active test; run experiments sequentially, not in parallel.
• Smart product sorting — while a template A/B test is active, it takes precedence over the platform's internal smart-sort experiment (chytré řazení in A/B mode); that experiment resumes when your test ends.
• First pageview included — the variant is assigned and rendered already on the visitor's first pageview, so landing-page changes can be tested too.
• Bots see the fallback — crawlers are never assigned a variant, so search engines index the stable fallback branch, not a random variant.