This page aggregates measured, corroborated evidence: donors' iPhones recorded apps contacting this domain, every claim below was reported by separate accepted donations and published under a human verdict (later rows for an approved app inherit its verdict). A contact is a measurement, not an accusation — it does not show what data was sent.
signin.costco.com
classified as first-party · 2
What our research panel found AI-drafted · human-reviewed
We ask several independent AI models the same question and publish their answers separately — cross-vendor agreement is evidence against fabrication, and disagreement is worth seeing. 3 of 3 models answered, overall confidence high. A human reviewed this domain's claims before anything here published.
Anthropic Claude — first-party
signin.costco.com is a subdomain of costco.com, the same brand as the app publisher (com.costco.costco), and its name indicates a first-party authentication/sign-in endpoint. First-party login traffic is consistent with the declared collection of Emails and App interactions, so nothing here implies an undeclared data flow.
OpenAI — first-party
The domain is a Costco subdomain and its signin hostname indicates first-party account authentication. The declared label includes relevant app interactions and email-related data, and the contact alone does not establish an undeclared data flow.
Google Gemini — first-party
The domain signin.costco.com is an explicit subdomain of the app's developer and brand, serving as a first-party authentication endpoint. Standard operational traffic to a first-party domain does not constitute undisclosed third-party tracking or data sharing.
Apps measured contacting this domain
| App | Label gap | Donations | Contacts | Seen |
|---|---|---|---|---|
| Costco Wholesale | — | 4 | 28 | 2026-07-28 → 2026-07-29 |
The corpus grows one report at a time: donate your App Privacy Report — anonymous by design.
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