Legal

Privacy Policy

Koboshi is a place to keep the words you are learning. This policy explains, in plain words, exactly what we hold, why we hold it, who else touches it, how long it stays, and what you can make us do about it.

Effective: 2026-07-26 (beta)

1. The short version

We have never sold personal data, and we never will. There is no advertising business here to sell it to.
There are no ad pixels and no third-party trackers. The only measurement is Vercel’s cookieless page-view counting, which sets no cookies and stores no personal identifiers, so no consent banner is needed.
Your private writing in Koboshi, the notes you attach to words today and any journal feature we ship later, is never sold, never put into a commercial or research dataset, and never used for advertising.
Four companies process data for us. All four are named below, with the country their systems sit in.
You can ask for a copy of everything we hold about you, or ask us to delete all of it, and we will do it.

2. Who runs Koboshi

Koboshi is operated by an individual operator based in Japan, who is the controller of your personal data and the person accountable for it. The operator's name and address are provided without delay upon request to support@koboshi.app. We do not publish them here, because a solo operator's home details would otherwise sit on a public page forever; ask and you get them, in writing, promptly.

For anything in this policy, including access, correction, export, deletion, objection, or a complaint, contact support@koboshi.app. That address reaches the operator directly.

3. What we hold, why, and for how long

Every category of personal data Koboshi holds is in this table, with the purpose we use it for, the legal basis we rely on, and how long it stays. Nothing is left out.

Category	Why we use it	Legal basis	How long we keep it
Account identity Your email address, and the basic profile Google returns if you sign in with Google.	To create your account and sign you in.	Performance of our contract with you (GDPR Art. 6(1)(b)). Under Japan’s APPI this is a stated purpose of use.	While your account exists. Deleted within 30 days of your deletion request.
Survey answers and settings What you tell us during onboarding or a retake (nickname, languages, self-rated level, study pace), plus your settings: timezone and interface language.	To set up your language pairs, pick your starting difficulty, decide what counts as "today", and render the app in your language.	Performance of our contract with you (Art. 6(1)(b)).	While your account exists. Change any answer by retaking the survey in Settings.
Month and year of birth Two dropdowns during setup. We never ask for the day; what is saved is a single value like "1998-04".	To check you are old enough to use Koboshi. The minimum is 13, applied the same everywhere.	Compliance with our legal obligations on children’s data (Art. 6(1)(c)), and our legitimate interest in not running a service for children (Art. 6(1)(f)).	While your account exists, and deleted with it. If the answer is under 13, setup stops, nothing else about you is saved, and the account is removed.
Heritage-speaker status A voluntary per-language marker saying you grew up around that language. Nothing in the service is withheld if you leave it unset.	To adjust the difficulty of the words we show you in that language, and nothing else.	Your explicit consent (Art. 6(1)(a) and Art. 9(2)(a)): it can hint at family background, so we treat it as sensitive and only store it if you tick the box. Untick it and we store nothing.	While your account exists, with a record of when you agreed and to which wording. Withdraw any time in Settings ("Remove my heritage answer"); that deletes both together.
Vocabulary and review history The words you save, their meanings and your notes, plus the full record of your reviews and quiz answers: what you answered, whether it was right, and when.	To run spaced repetition, decide what is due, and show you your own statistics and streaks.	Performance of our contract with you (Art. 6(1)(b)).	While your account exists. Deleted with the account.
Usage events and daily caps A small in-app log of what happened (an event name, a timestamp, a few plain fields), and per-day counts of your AI lookups and screenshot extractions.	To see which features are used, find bugs, and enforce the beta fair-use caps.	Our legitimate interest in operating and improving Koboshi (Art. 6(1)(f)). You can object; see "Your rights".	While your account exists, and deleted with it.
Push notification subscription If you turn on study reminders: the push endpoint your browser issues, its encryption keys, and your browser user-agent.	To send the daily study reminder you asked for. Nothing else is ever sent to it.	Your consent (Art. 6(1)(a)), confirmed in Settings before your browser’s own permission prompt appears.	Until you turn reminders off in Settings, which deletes the stored endpoint and unsubscribes the browser.
Word flags (report a problem) When you flag a card: the category, any free text you typed, and a snapshot of what was on screen (the fields shown, quiz mode, screen size, platform, app build).	So the operator can reproduce and fix a wrong or badly rendered dictionary entry. Read by the operator only.	Our legitimate interest in keeping the shared dictionary correct (Art. 6(1)(f)).	While your account exists, and deleted with it. Please do not type personal information into the free-text box.
Flag screenshots For some flag categories, a small JPEG of the flagged card itself, captured from the card’s own element, never from your window, screen, or other tabs. Private bucket; only the operator can read it.	Because a broken layout usually cannot be diagnosed from field values alone.	Our legitimate interest in fixing rendering faults you report (Art. 6(1)(f)).	14 days. A scheduled sweep deletes every older capture automatically.
Screenshot extraction images If you use "add words from a screenshot", the image is downscaled in your browser and sent to our AI provider to read the words. Koboshi never stores it.	To pull vocabulary out of a picture you chose to upload.	Performance of our contract with you (Art. 6(1)(b)).	Zero, on our side. Anthropic deletes inputs and outputs within about 30 days under its own policy. Please crop out other people’s information before uploading.
Server logs Standard technical logs kept by our hosting and database providers: IP address, request time, and the page or function requested.	Security, abuse prevention, and diagnosing outages.	Our legitimate interest in keeping the service secure and working (Art. 6(1)(f)).	Under our providers’ own retention settings; we do not build user profiles from these logs.

The table above is the whole disclosure. What it is called where you live differs slightly:

European Economic Area and the United Kingdom. The legal-basis names in the table come from the EU and UK GDPR. Your rights, and how to actually use them, are in section 8.
Japan. The same table doubles as the statement of our purposes of use under the APPI, and section 6 names every country your data is processed in.
United States, including California. The same table doubles as the categories and purposes disclosure. We have never sold personal data, and we do not share it for cross-context behavioral advertising.
Everywhere else. The rights in section 8 are offered to everyone, wherever you live.

4. The heritage-speaker question

You can mark a language you already speak as one you grew up around. It is voluntary, nothing is locked behind it, and we use it for one thing: choosing how hard the words we show you in that language should be. Because it can hint at your family background, it is only stored if you tick a consent box next to a plain explanation; leave the box unticked and nothing is saved at all.

Taking it back is one click: Settings, then Onboarding, then "Remove my heritage answer". That deletes the marker and the consent record together, and nothing else about your account changes.

5. Screenshots: two different things

Adding words from a screenshot. The image you pick is shrunk in your browser and sent to our AI provider to read the words in it. Koboshi never stores that image. Anthropic deletes inputs and outputs within about 30 days under their own retention policy. Please crop other people out before you upload.

Screenshots attached to a problem report. Some flag categories capture a small image of the flagged card itself, never your window or screen, so it cannot include your status bar or other apps. It goes into a private bucket only the operator can read, and it is automatically deleted after 14 days.

6. Who else processes your data, and where

Four companies process data on our behalf. All of them are in the United States, so your data leaves your country and, if you are in Japan or the EU or the UK, it crosses a border. Here is exactly who, for what, where, and on what safeguard.

Provider	What they do for us	Country	Transfer safeguard
Supabase	Database, authentication, and file storage. Holds your account and all of your learning data.	United States	Data processing agreement with EU standard contractual clauses.
Vercel	Hosting for the website, the app, and the small server functions that talk to the AI provider. Also counts page views for us, without cookies and without storing personal identifiers.	United States	Data processing agreement; EU-US Data Privacy Framework certified, with standard contractual clauses as a backstop.
Anthropic	The AI model that generates word meanings, examples, and reads uploaded screenshots.	United States	Data processing agreement with standard contractual clauses. Your content is not used to train their models.
Google	Sign in with Google (optional), and Cloud Text-to-Speech for pronunciation audio in some languages.	United States	EU-US Data Privacy Framework certified, with standard contractual clauses as a backstop. For sign-in, Google acts on its own account as well as ours.

These are the only four. We do not share your personal data with anyone else, we do not sell it, and we do not share it for cross-context behavioral advertising. We would disclose data if a valid legal order required it, and we would tell you unless we were forbidden from doing so.

7. Cookies, local storage, and session storage

Koboshi sets no advertising cookies and runs no trackers, so there is no consent banner to click. What the app stores on your own device, all of it needed to make the app work: your sign-in session, in-progress survey answers, today’s screenshot count, whether you dismissed the install prompt, and which notices you have seen (kept until you sign out or clear browser data); plus the lookup queue, the quiz in progress, and your last review filter (cleared when you close the tab). If you install Koboshi as an app, its service worker also caches the app’s program files on your device; that cache holds no personal data.

8. Your rights, and how to actually use them

Wherever you live, you can ask us to: give you a copy of everything we hold about you; correct anything that is wrong; export your data in a machine-readable file; delete your account and its data; stop processing that rests on our legitimate interests, including usage events; or withdraw a consent you gave, such as the heritage marker or push reminders.

Much of your data is editable in the app already: your survey answers through a retake, your saved words and notes directly, and push reminders through the Settings switch. Withdrawing the heritage consent is its own one-click action in Settings, under Onboarding, described in section 4. Export and deletion are self-serve: in the app, open Settings, then "Download my data" or "Delete my account". You can also email support@koboshi.app and we will do it by hand. We answer within 30 days, and there is no charge. We may ask you to confirm the request from the email address on the account, so that nobody else can request your data.

Deletion means the account and everything keyed to it: your words, your review and quiz history, your survey answers, your preferences, your usage events, your flag reports, and your push subscription. Shared dictionary entries stay, because they carry nothing that identifies you.

If you think we have handled your data badly, please tell us first at support@koboshi.app and we will look into it. You can also complain to a regulator: in the EU, your national data protection authority; in the UK, the Information Commissioner’s Office, and you are entitled to complain to us first and receive an acknowledgement; in Japan, the Personal Information Protection Commission; elsewhere, your local privacy regulator.

9. Security

Connections are encrypted in transit, and every table is protected by row-level security so an account can only ever read its own rows. Flag screenshots sit in a private bucket that is not readable by other users. API keys live only in server environment variables and never reach your browser. The operator is the only person with administrative access, and a small number of routine maintenance jobs run with elevated access on a schedule.

No system is perfectly secure, and we will not pretend otherwise. A deleted account can persist in our database provider’s encrypted backups for a short period before those snapshots roll over; backups are used for disaster recovery only and are never restored to bring back deleted data.

10. Children

Koboshi is for people aged 13 and over, and it is not directed at children. Setup asks for the month and the year you were born, in a plain question that does not tell you what answer gets you in, and an answer under 13 cannot finish setting up. If we learn that an account belongs to someone under 13, we delete it and its learning data. If you are a parent or guardian and believe your child has an account, email support@koboshi.app and we will remove it.

11. If something goes wrong

If a security incident affects your personal data, we will tell you without undue delay, in plain language, describing what happened, what data was involved, and what you should do. We will notify the relevant supervisory authorities wherever the law requires it, within the deadlines those laws set. We keep an internal record of incidents, including ones we conclude are not reportable.

12. Automated decisions and profiling

Koboshi schedules your reviews automatically using a spaced-repetition algorithm, and it picks word difficulty from your stated level. That is the product working as intended. We do not make decisions about you that carry a legal or similarly significant effect, and we do not profile you for advertising, credit, employment, or anything of that kind.

13. Changes to this policy

We will update this page when the service changes, when a provider changes, or when the law changes. The effective date at the top always tells you which version you are reading, and every past version is kept in our public source history so you can see what changed and when. For a change that materially reduces your privacy, we will tell you in the app or by email before it takes effect, rather than quietly editing this page. We will never apply a reduced protection retroactively to data we already hold under the old terms.

14. Contact

Privacy questions, data requests, complaints, or a request for the operator's name and address: support@koboshi.app. A person reads it, not a ticket queue.