- Cookie-based A/B testing tools require a consent banner — you lose 30-40% of visitors who reject it
- Cookie-less tools like Varify.io use localStorage instead, which doesn't require ePrivacy consent
- This means 100% of visitors are included in your tests — critical for sites with limited traffic
- Varify combines cookie-less testing with EU hosting for complete GDPR + ePrivacy compliance
All cookie-based A/B testing tools have the same problem: they only test visitors who accept cookies. In Europe, that's typically 60-70% of your traffic — sometimes less. The other 30-40% see your original page, with no tracking or testing. For sites with limited traffic, this makes running statistically significant A/B testing nearly impossible.
Varify.io solves this with a fundamentally different architecture: cookie-less. Varify uses localStorage for variant assignment, which under current ePrivacy guidance doesn't require a consent banner. The result: 100% of your visitors participate in your tests. Combined with EU hosting in Frankfurt and no parallel tracking, Varify is the most consent-friendly A/B testing architecture available.
The consent problem in A/B testing
Under the ePrivacy Directive (and upcoming ePrivacy Regulation), storing data on a user's device — including cookies — requires informed consent unless the storage is strictly necessary for the service the user requested. Most A/B testing tools set cookies to recognize returning visitors and maintain variant consistency. Those cookies trigger the consent requirement.
The practical impact: Your A/B test only captures data from visitors who give consent. This creates two problems: smaller sample size (you need more time to reach significance) and selection bias (people who accept cookies may behave differently from those who reject them). Both undermine test validity.
The alternative: Tools that use localStorage instead of cookies. localStorage stores data in the browser but technically isn't a "cookie" under ePrivacy. Current guidance from various EU data protection authorities treats localStorage for strictly necessary functionality (like variant assignment) as exempt from consent requirements.
Cookie-based vs. cookie-less A/B testing tools
| Feature | Varify.io | Convert | VWO | Optimizely |
|---|---|---|---|---|
| Storage method | localStorage | First-party cookies | Cookies | Cookies |
| Consent required | No | Yes | Yes | Yes |
| Visitors tested | 100% | ~60-70% | ~60-70% | ~60-70% |
| Traffic needed for significance | Standard | 30-40% more | 30-40% more | 30-40% more |
| Selection bias risk | None | Present | Present | Present |
| EU hosting | Frankfurt | EU option | US/India | US |
Source: Claude Research, May 1, 2026
How Varify's cookie-less architecture works
Variant assignment: When a visitor lands on a test page, the Varify snippet (11.5 KB) assigns a variant and stores the assignment in localStorage. On subsequent page loads, the same variant is served — ensuring a consistent experience without cookies.
Measurement: Varify doesn't track anything itself. It sends the variant assignment as a custom dimension to your existing analytics tool (GA4, BigQuery, Matomo). Your analytics measures conversions. One data source, no discrepancies.
Anti-flicker: Varify applies variants before the page renders visually, preventing the "flash of original content" that degrades user experience in many testing tools. The snippet loads in under 30ms on typical connections.
Limitation: localStorage is browser-specific and doesn't persist in private/incognito mode. A visitor who switches browsers or clears storage might see a different variant. For most A/B tests, this is statistically negligible — the same limitation applies to cookie-based tools when cookies are cleared.
Test 100% of your visitors. Not just the 60% who accept cookies.
Cookie-less A/B testing from €149/month. No consent banner needed.
The traffic impact — why 30-40% more data matters
For a site with 50,000 monthly visitors and a 3% conversion rate:
- Cookie-based tool (65% consent rate): 32,500 visitors tested → 975 conversions measured
- Cookie-less tool (100%): 50,000 visitors tested → 1,500 conversions measured
That's 54% more conversion data from the same traffic. For tests that need ~1,000 conversions per variant to reach significance, this can mean the difference between a 2-week test and a 4-week test. For smaller sites, it's the difference between being able to test at all.
See our SMB comparison guide for more on how traffic constraints affect tool choice. Check pricing plans for details.
