We graded ourselves against Mozilla’s own standard — on purpose.
In 2026, Mozilla’s *Privacy Not Included guide reviewed six popular period-tracking apps for exactly what they collect, who they share it with, and what happens to it. Only one — Euki — earned a perfect score. Most privacy pages are a promise you can’t check. This one is built to be checked: we applied Mozilla’s published criteria to our own code, honestly, and we’re publishing the result — including the parts we haven’t fully solved yet.
Last updated August 2026
What Mozilla actually measures
Their team doesn’t just read privacy policies — they run manual use and network-traffic analysis, partner with Harvard’s Berkman Klein Center on policy-history review, and had university researchers test the Android builds directly. The line from their report that matters most:
“Data minimization is stronger than a promise not to misuse data.” A company that never collects a centralized health record can’t sell it, can’t be breached at scale, and can’t be compelled to hand it over — no policy language substitutes for that.
Here’s how the six apps Mozilla reviewed actually scored:
| App | Score | What determined it |
|---|---|---|
| Euki | 10/10 | No account, no cloud sync, data never leaves the device. Open-source, nonprofit-run. |
| Clue | 8/10 | Meaningful consent separation, but external providers could still infer a device was running Clue from contextual signals. |
| Flo | 7/10 | Device identifiers reached an ad-analytics vendor before “Anonymous Mode” could even be turned on. |
| Period Calendar | 6/10 | Ad-supported — device ID, screen size, and timezone sent to ad networks, enough to infer reproductive-health details. |
| Spot On (Planned Parenthood) | 5/10 | Provider search leaked city, care type, and last-period date to a third-party analytics vendor. |
| Stardust | 2/10 | Logged symptoms went straight to an analytics vendor with a persistent user ID attached. |
Arte & Cera, against the same rubric
Mozilla didn’t review us — this is a self-assessment against their published methodology, not an official score. Every line below is checkable against our actual code and database, not just what our policy claims to do.
Third-party trackers & ad SDKs
Scoped, by designWe use one product analytics tool (PostHog) to understand how people use the general, non-health parts of the site. It runs on an allowlist, not a blocklist: the code enumerates exactly which pages are ever tracked — things like the homepage and the rewards page — and every page where you view or enter health information (assessments, the cycle tracker, the maternity companion, labs, your account) is excluded by default, the same way a route we haven’t written yet would be excluded by default too, not just the ones we remembered to block. That exclusion covers individual education articles and supplement pages too — the article title itself is health information — so only the general education and supplements hub pages are ever tracked, never a specific article or stack. No ad SDKs exist anywhere in our code — this is a scoped analytics vendor, not an advertising one, and it never receives anything from a health page. That’s a real, meaningful difference from Euki’s zero-analytics baseline, and we’d rather say so plainly than claim parity we don’t have.
Data sale to brokers
PassStructurally true, not just promised — there’s no ad-tech vendor relationship anywhere in our stack a data-broker deal could even run through.
Location data
PassWe don’t collect geolocation anywhere in the app — the exact signal that made Spot On’s provider-search leak so damaging. Nothing in our systems could place someone at a clinic. That includes PostHog, our analytics vendor: it derives country/city-level location from IP address by default, so we explicitly turned that off rather than leave it as an unmentioned side effect of adding an analytics tool.
Law-enforcement & subpoena posture
PassOur privacy policy names Washington’s My Health My Data Act specifically, explains what legal process we can and can’t resist, and commits to notifying you when legally possible — more specific than the boilerplate most apps in this category use.
Consent model
PassWashington’s My Health My Data Act requires collection and sharing consent as “separate and distinct” affirmative acts, not one bundled checkbox most apps use. We built it that way, with every consent event tied to the exact policy version shown at the time.
Your control — export & deletion
PassA real, working data export — assessments, cycle logs, mood check-ins, maternity data, lab requests, all in one readable file, from your Account page any time. Account and data deletion available on request.
Local-first for anonymous use
PassYou don’t need an account to use the cycle tracker. Log without signing in and your entries stay on your device, genuinely — nothing is sent to us until you decide to save. If you sign in later, you’re offered the choice to bring that local data into your account, rather than losing it silently.
Encryption for the most sensitive data
PassEncryption in transit and at rest are standard across our infrastructure. On top of that, the specific content of self-assessment answers and mood check-ins — including anything mental-health related — is encrypted a second time at the application layer, so even direct database access exposes only ciphertext, not readable answers.
Error-monitoring data hygiene
PassOur crash-reporting tool is configured to never receive your IP address, cookies, or request data by default, and to scrub known-sensitive field names out of anything it does capture — the kind of unscrubbed side channel that Mozilla’s methodology is specifically built to catch, closed before it could ever leak anything.
Vulnerability disclosure contact
PassA published, monitored security.txt gives security researchers a real way to reach us in good faith — one of Mozilla’s five baseline Minimum Security Standards.
Centralized account model
Open, by designThis is the one honest gap left, and it’s architectural, not a mistake. Data you save to your account lives in one database, tied to your account — the shape Mozilla’s own framing calls higher-risk by default, because a centralized record is the thing that could theoretically be sold, breached in bulk, or subpoenaed. We built it this way on purpose, because it’s what lets you sync across devices, get a follow-up if an assessment result is concerning, and use the maternity companion the way it works today — and we’ve encrypted, minimized, and rights-protected that data as much as a centralized model reasonably allows. But it’s not the same as never having the data at all, and we’d rather say that plainly than paper over it.
Attorney-reviewed policy
In progressOur privacy policy is unusually specific for this category, and it says so itself: it’s an accurate description of current practice that hasn’t yet had a formal legal review, given the MHMDA-specific claims it makes. That review is in progress.
Where does that leave us? We don’t tie Euki’s 10/10 outright — we run one scoped analytics vendor and a centralized, account-based service, and Euki runs neither. But we’re not in the same category as Clue, Flo, Period Calendar, Spot On, or Stardust either: every one of those apps let health-page data — symptoms, provider searches, logged results — reach an ad or analytics vendor. Ours structurally can’t, by an allowlist enforced in code, not a policy promise. That’s a real middle position, not a perfect score, and we’d rather describe it accurately than round it up to “we’re just like Euki.”
Sources: Mozilla Foundation, *Privacy Not Included — Period and Ovulation Apps Privacy Review and the Euki product review, mozillafoundation.org/en/privacynotincluded. Arte & Cera figures are drawn directly from our own dependencies, database schema, and current privacy policy as of the date above — not from aspirational claims. This page is a self-assessment, not an endorsement by or affiliation with Mozilla.