Conversion Optimization

GrowthBook

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Panel rating · 6 judges · How to read the stars

Category median

Sovereignty: 1 of 4 dimensions proven

0–5 in half steps. 5 means the rubric's top anchor is met on the evidence.

An AI-assisted analysis of public evidence — not a hands-on test.

Every score, rationale and verdict on this page is AI-generated. Every claim cites the source it was read from. Nothing here is a human star review — and no score can be bought. How scores are made →

Method and versions

The Growth Lead v1.0 · The E-Commerce Manager v1.0 · The Product Engineer v1.0 · The CRO Consultant v1.0 · The Data Protection Officer v1.0 · The Skeptic v1.0 · rubric v1 · evaluated 5 Oct 2026

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Read this page as one judge. Each weighs the same scores by what they care about.

The Skeptic

Weighted verdict

A statistician who has watched too many "winners" regress to zero. Reads for the method by name, what stops a team from peeking, sample ratio mismatch checks and multiple-comparison corrections — and treats a "probability to beat" without documented assumptions as marketing.

Same scores as the panel view — this lens weights them the way this judge cares.

Scored by The Skeptic

Experiment types & delivery

How this is scored

What can be tested and where: client-side changes through an editor, server-side and feature experiments through SDKs, multivariate and multi-page tests, and personalisation — judged on what the documentation shows rather than on the feature grid.

0 — Simple A/B split of one page element through a visual editor; no server-side option, no targeting beyond URL.

3 — Client-side A/B and split-URL tests with basic audience targeting, and no SDK or server-side delivery.

5 — Client-side and server-side experiments through documented SDKs for common languages, multivariate and multi-page tests, audience targeting on behaviour and attributes, and rule-based personalisation.

8 — Feature-flag-based experiments sharing one audience and metric model with web tests, mutually exclusive experiment groups, holdouts, edge or CDN delivery, and personalisation that can itself be tested against a control.

10 — One experimentation programme across every surface: web, app, server and edge from the same platform, experiment interactions managed, a documented experiment lifecycle from hypothesis to archived result, and a library of past results a team can search.

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The Skeptic

Visual editor and URL redirects, server-side experiments through feature-flag rules or inline SDK code, custom assignment analysis, holdouts and namespaces for mutual exclusion, 24-plus SDKs spanning server, client, mobile and edge, and a documented edge app on Cloudflare and other providers that evaluates flags before HTML ships. We found no public information on rule-based personalisation that can itself be tested against a control, nor a searchable library of past experiment results, which is what holds this back. 1 6 7 11 12

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Statistical method & guardrails

How this is scored

Which statistics decide the winner and what protects the customer from misreading them. Scored on what the vendor documents: the method by name, how peeking and multiple comparisons are handled, and whether sample ratio mismatch is detected.

0 — A "winner" or "probability to beat" figure with no documented method, no stated sample-size guidance and no warning against stopping early.

3 — The method is named (frequentist or Bayesian) but its assumptions are not documented, and nothing prevents a test from being called while it is still underpowered.

5 — Documented method with confidence or credible intervals, a sample-size or test-duration calculator, and stated guidance on when a result may be read.

8 — Sequential testing or an equivalent documented protection against peeking, correction for multiple metrics or variants, sample ratio mismatch detection, variance reduction such as CUPED, and guardrail metrics that can stop a harmful test.

10 — The statistics are auditable: methodology published in enough detail to reproduce a result, the choice of method explained per use case, raw per-visitor data available for independent re-analysis, and the interface refuses to present an underpowered result as a conclusion.

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The Skeptic

Both engines are on the record with their assumptions — Bayesian with a documented default improper prior and an optional proper Normal prior, frequentist as two-sample t-tests on relative change — alongside sample ratio mismatch detection, CUPED, guardrail metrics, minimum data rules and a power calculator, with an open-source implementation a result can be checked against. My reservations: the multiple-comparison corrections exist only for the frequentist engine while Bayesian is the default, sequential testing appears as a listed test type without the peeking mathematics documented, and adjusted p-values can be exported only as CSV, not through the API. 2 6 7 8 9

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Consent & visitor tracking

How this is scored

Whether the test script respects §25 TDDDG and the ePrivacy rules as evidenced on the vendor's own pages: when the script runs relative to consent, what it stores on the device, whether a cookieless or consent-free mode exists, and how visitor identifiers are handled.

0 — Nothing on the vendor's pages says what the script stores on the device or whether it runs before consent; consent is described as the customer's problem.

3 — Cookies or local storage are listed, and a consent integration is mentioned, but the documentation does not say what the script does before consent is given.

5 — Documented behaviour before and after consent, integration with common consent management platforms, a published list of cookies and storage keys with their lifetime, and IP anonymisation described.

8 — A documented consent-pending mode that holds tracking until consent while variants can still be served, a cookieless or first-party-only option, retention of visitor data stated, and guidance on the legal basis for testing in the EU.

10 — Built for §25 TDDDG: the default configuration stores nothing on the device without consent, a server-side or cookieless mode documented end to end, per-visitor data deletable on request, and the vendor states in writing how each mode maps to consent requirements.

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The Skeptic

The consent mechanics are documented in implementable detail: a first-party identifier cookie the edge server does not write by default, a documented setting plus a JavaScript event that delay cookie persistence until consent, and hash-based assignment that works with no cookie at all. Less complete: we found no published cookie lifetimes, nothing on IP anonymisation or consent management platform integration, and the privacy notice states DNT signals are not honored. 3 6 11 12

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Snippet performance & flicker

How this is scored

The cost the client-side snippet imposes on the page it tests: blocking load, flicker of original content, script weight and the effect on Core Web Vitals — scored on what the vendor measures and publishes, not on "lightning fast".

0 — A synchronous snippet with no stated size, no flicker handling and no mention of performance.

3 — An anti-flicker snippet that hides the page until the test loads, with a timeout, and no published figures for script size or load cost.

5 — Script size and loading behaviour documented, asynchronous loading option, flicker handling explained with its trade-off, and CDN delivery of the snippet.

8 — Published performance figures including impact on Core Web Vitals, a self-hosting or first-party-domain option for the script, per-project bundles containing only active experiments, and a server-side or edge alternative for flicker-sensitive tests.

10 — Performance is a stated commitment: measured overhead published and maintained, flicker eliminated by edge or server-side rendering as a documented path, and tooling that shows the customer what their own configuration costs the page.

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The Skeptic

To its credit the edge documentation states plainly that the default mode makes a blocking API call on every user request, then documents two ways to remove it — a push model into an edge key-value store or a just-in-time payload cache — plus a self-hosted proxy with your own CDN and payload endpoints scoped to a single environment or project; edge and hybrid delivery is documented as eliminating redraw flicker for visual and redirect tests. What is missing for a higher mark: no published script sizes or Core Web Vitals figures, only a relative claim of fifty percent smaller SDKs. 1 11 12 14

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Analytics, data export & integrations

How this is scored

Getting results and raw data out: integration with analytics and tag management, export of visitor-level results, warehouse-native analysis, and an API — because an experiment result that cannot be checked in the customer's own data is a claim, not a finding.

0 — Results visible in the vendor's dashboard only; no export, no analytics integration, no API.

3 — CSV export of aggregated results and one analytics integration, with no visitor-level data and no documented API.

5 — Integrations with common analytics and tag managers, export of results, and a documented API for managing experiments and reading results.

8 — Visitor-level raw data export or streaming to a data warehouse, warehouse-native analysis on the customer's own metrics, CDP integration for audiences, and an API with stated limits.

10 — The platform treats the customer's warehouse as the source of truth: metrics defined once and computed there, full historical experiment data exportable in open formats, and a versioned API a team can build its own programme tooling on.

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The Skeptic

Warehouse-native is the design, not a bolt-on: metrics are defined in SQL and computed in the customer's own Snowflake, BigQuery, Databricks or Redshift, every query is visible, results are described as reproducible, and a full REST API with versioned endpoints covers experiments, results, fact metrics, segments and feature toggles. The nits: adjusted p-values are exportable only as CSV rather than through the API, and we found no stated API rate limits or a CDP audience integration. 2 5 7 9 13 14

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European sovereignty

How this is scored

Where visitor data is processed and stored and who the contracting entity is. Independently sourced by the sovereignty pipeline; weighted higher here than in categories that hold only the customer's own data, because the script runs on every visitor to the customer's site and their behaviour is what the platform records.

0 — Non-EU vendor and contracting entity, hosting unstated, subprocessors unnamed, and visitor data leaving the EU without a stated safeguard.

3 — EU data residency offered as an option or an enterprise add-on while the contracting entity is non-EU, or the subprocessor list is absent.

5 — EU processing of visitor data as standard and an EU contracting entity, but parts of the chain — CDN, support access, analytics — are non-EU without an explained safeguard.

8 — EU hosting on named infrastructure including the delivery of the snippet, EU contracting entity, subprocessor list published, and a DPA covering the visitor data the script collects.

10 — Sovereign end to end and evidenced: vendor, entity, hosting, snippet delivery and every subprocessor European, certification published, and no visitor data reaching a non-EU party at any point.

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The Skeptic

A California contracting entity under California law, processing described as held in the United States with visitors consenting to that transfer, US AI providers named as subprocessors for optional features, no published subprocessor list and no stated transfer safeguard. The sole mitigation on the vendor's pages is the self-hosted, air-gapped deployment where no data leaves your own system; everything captured about the hosted offering points away from European sovereignty. 3 4 5 10

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Pricing transparency

How this is scored

A category priced by traffic — monthly tracked users, visitors or impressions — where the tier a site lands in depends on numbers the buyer has to estimate. Whether a buyer can compute the real annual cost including traffic limits, overage, server-side or personalisation modules and seats — from public pages alone.

0 — No public prices at all; every tier is a sales conversation.

3 — A starting price or a free tier exists, but the traffic metric, the limits and what happens above them are unstated — the invoice is unknowable.

5 — Tier prices public with the traffic metric and its limits defined, but at least one commonly needed piece (server-side SDKs, personalisation, overage) is unpriced or "contact sales".

8 — Every tier priced publicly with the traffic metric defined, limits, overage rates, module prices, minimum term and VAT treatment stated.

10 — Complete price computability: annual invoice derivable for a given traffic volume, set of modules and team size, with overage and every add-on published.

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The Skeptic

Starter is free without a credit card, Pro is published at $40 per seat per month for up to 30 users, and — unusually for this category — traffic is published as unlimited, so the invoice hinges on seats and the metered extras. Those extras carry published limits and overage figures for managed warehouse events, CDN bandwidth and CDN requests, but Enterprise is a sales conversation and we found no public information on minimum term or VAT treatment. 2 7

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European sovereignty — proven facts

1 of 4 dimensions proven

Built only from facts shown on the vendor's own pages. A dimension we could not prove is left open, not scored as zero.

Legal entity	Not determined	—	uncited Report an error
Ownership	Not determined	—	uncited Report an error
Data residency	Not determined ⚠ unverified	—	uncited Report an error
Subprocessors	US CLOUD Act reach ⚠ unverified	0/2 pts	5 Report an error

Where this could be wrong

Evidence ages. The oldest capture behind this page is from 22 Sep 2026. Vendors change pricing and policies without notice; every fact reflects its source as of the capture date shown in the registry.
Weak sourcing — Data residency. Not confirmed on the vendor’s own pages as captured.
Weak sourcing — Subprocessors. The privacy notice also names US AI providers (Anthropic, Google, OpenAI, xAI) as sub-processors for optional AI features, and the managed warehouse stores event data on 'ClickHouse infrastructure', all without stated server regions.
AI can misread a source. Extraction and judgement are automated; a citation guarantees traceability, not infallibility. If something here is wrong, say so — no account needed, every report is decided within 5 business days, and accepted corrections are published.

What we left out

A claim that does not survive our checks costs us the claim, not the page. This is what was taken off this one.

17 product facts could not be confirmed on the vendor’s page as captured and were left out of this page and of the panel’s material. Know more? Tell us
5 integrations facts could not be confirmed on the vendor’s page as captured and were left out of this page and of the panel’s material. Know more? Tell us
3 legal facts could not be confirmed on the vendor’s page as captured and were left out of this page and of the panel’s material. Know more? Tell us
3 pricing facts could not be confirmed on the vendor’s page as captured and were left out of this page and of the panel’s material. Know more? Tell us
2 compliance facts could not be confirmed on the vendor’s page as captured and were left out of this page and of the panel’s material. Know more? Tell us
1 support fact could not be confirmed on the vendor’s page as captured and was left out of this page and of the panel’s material. Know more? Tell us
1 sovereignty dimension could not be confirmed on the vendor’s own pages and is shown as unknown. Know more? Tell us

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Sources (14)

The pages every claim on this page was read from — each one checked, dated, and kept verifiable.

1 Vendor homepage www.growthbook.io Checked 22 Sep 2026 Details →
2 Pricing page www.growthbook.io Checked 22 Sep 2026 Details →
3 Privacy policy www.growthbook.io Checked 22 Sep 2026 Details →
4 Terms of service www.growthbook.io Checked 22 Sep 2026 Details →
5 Security / trust page www.growthbook.io Checked 30 Sep 2026 Details →
6 Experiment types & delivery — found from sitemap docs.growthbook.io Checked 1 Oct 2026 Details →
7 Experiment types & delivery — found from sitemap www.growthbook.io Checked 1 Oct 2026 Details →
8 Statistical method & guardrails — found from sitemap docs.growthbook.io Checked 1 Oct 2026 Details →
9 Statistical method & guardrails — found from sitemap docs.growthbook.io Checked 1 Oct 2026 Details →
10 Consent & visitor tracking — found from sitemap www.growthbook.io Checked 1 Oct 2026 Details →
11 Snippet performance & flicker — found from sitemap docs.growthbook.io Checked 1 Oct 2026 Details →
12 Snippet performance & flicker — found from sitemap docs.growthbook.io Checked 1 Oct 2026 Details →
13 Analytics, data export & integrations — found from sitemap docs.growthbook.io Checked 1 Oct 2026 Details →
14 Analytics, data export & integrations — found from sitemap docs.growthbook.io Checked 1 Oct 2026 Details →