Kuai privacy policy
Last updated: 2026-10-27
Kuai is an Android app for learning languages. The data controller is Kuai Studio. In this page, "we" means Kuai Studio. You can reach us at support@kuaistudio.com.
The short version
- We keep what we need to run your account and sync your study. Nothing more.
- We show no ads and we do not sell your data.
- When you use an AI feature, the words you wrote or said go to our server and on to an AI company. We name each one below.
- Sending your voice, usage numbers or feedback only happens when you choose it.
- You can delete your account and your data in the app, or on the web, any time.
What we collect, and why
| What | Why | When it happens |
|---|---|---|
| A random account number. | So your study can sync and your AI allowance can be counted. | Automatically, when the app first needs sync or AI. You do not have to give a name or email. |
| Your email address, if you sign in with Google or with email. | So you can sign back in on another phone. | Only if you choose to sign in. |
| Your phrases, cards, review history, chats with your tutor, saved texts and a few settings. | So your study follows you to a new phone. | Automatically once you have an account. |
| The words you write or say to an AI feature, and the lesson text around them. | To grade, answer, explain and translate. | Only when you use an AI feature, and only after you confirm you are 18 or older. |
| A short recording of your voice. | To turn your speech into text. | Only when you tap the microphone and speak. |
| The address of a podcast episode. | To make a transcript. | Only when you ask for one. |
| How much AI you have used: counts, time, which task and how much it cost. | To keep to your daily and monthly allowance and our costs. | When you use hosted AI. |
| A scrambled version of your internet address (IP address). | To stop abuse, such as someone trying thousands of sign-ins. | On every request to our server. |
| Usage events: which screens you open and which goals you reach, plus a random install number. | To see what works and what breaks. | Only if you turn on "Share anonymous usage events". It is off until you do. |
| A note you write, the app version, your phone type and study language. Optionally an error log and a screenshot. | To fix problems you tell us about. | Only when you tap Send after seeing a preview. |
We do not collect your location, contacts, photos, files or calendar. We do not read your messages. Text recognition from a photo happens on your phone, and the photo is not uploaded. The text it finds can sync like any other text you add.
Who else handles your data
Cloudflare hosts our server, database and audio files and runs podcast transcription. Requests to these services include the data needed for the feature you use.
Our AI and voice providers are listed below. They receive the words, lesson context or audio needed for the feature. Their own processing and retention terms apply.
- Google Gemini
- Groq Whisper
- Alibaba Qwen
We will update this policy before moving a task to another AI provider.
Your phone also talks directly to some services when you use the matching feature: YouTube (to show and read a video and its captions), Apple's podcast directory (to search for a podcast), websites and feeds you paste in, Google Fonts, and Google Play services (to download a text-recognition model). We do not see those requests. They see your internet address and what you asked for, and their own policies apply. YouTube's player may set its own cookies and IDs on your phone.
Your voice
You can speak to Kuai to practise. The first time, Android asks for the microphone permission. You can say no and use the app by typing.
When you speak, Kuai records a short clip (up to 30 seconds) and sends it to our server, which passes it to our speech recognition provider to turn it into text. We do not save the clip or the text, and we do not write them to our logs. We only count the seconds. The speech recognition provider does not keep your data by default, but it may keep a log of requests for up to 30 days to find faults and abuse, unless zero retention is switched on. It stores any data it keeps in the United States. Provider terms govern any further processing.
If our server is not available, Kuai uses the speech recogniser on your phone instead, but only on Android 12 and later. On older phones you will need to type.
Accounts and sync
Kuai makes you an anonymous account without asking for a name or email. It has a random number and nothing else that says who you are. That number is what syncs your study.
You can also sign in with Google or with an email and password. Then we keep your email address (and for email sign-in, a scrambled form of your password that we cannot turn back into the password), so you can sign in on a new phone. For email accounts, password reset is not available yet, so keep your password safe.
What syncs: your phrases and cards, your review history, a few settings, your tutor chats, and the texts, books and sources you saved. We never sync a personal AI key.
Usage analytics (only if you turn it on)
This is off until you turn on "Share anonymous usage events" in Settings → Account, sync & backup → Privacy. When it is on, Kuai sends the name of a screen or goal (for example "finished a session"), a time, and a random install number. It never sends what you write or say, and it does not include your account number. Turning it off removes the install number from your phone. Events that have not been sent are dropped after 7 days. Hourly cleanup deletes server events after 90 days. We keep daily totals that have no install number in them.
Crash reports and feedback
If Kuai crashes, it saves a short technical note on your phone: the code path, with no message text and nothing you wrote. It keeps the last three. Nothing is sent unless you attach one when you send feedback.
When you send feedback, you see exactly what will go before you tap Send: your note, the app version, phone type, study language, and, if you add them, an error log and a screenshot. Please do not put passwords or private details in a note or a screenshot.
Our abuse checks
To stop people hammering our server, we count requests per scrambled internet address and per account for a minute at a time. The scrambling (a SHA-256 hash with no secret added) is not strong, so please treat it as your internet address in practice. Cloudflare, which runs our network, also sees your real internet address as part of delivering the app. We do not use your internet address to work out where you are.
How long we keep things
| What | How long |
|---|---|
| Account, synced study data, chats, saved texts | Until you delete your account |
| AI cost and allowance records with your account number | Until you delete your account |
| Daily cost totals (no account number) | Kept |
| Records of an AI request (a fingerprint, status and cost) | 10 minutes |
| Your voice clips and their text | Not kept by us. Our speech recognition provider may log for up to 30 days. |
| Podcast audio | Not kept. A private transcript is delivered to you once and then deleted from our server. Transcripts of public podcasts are kept to save cost. |
| Speaking-check session records | 31 days |
| Usage events | 90 days |
| Feedback, error logs and screenshots you send | Until you delete your account |
| Counters with a scrambled internet address | About a minute, then removed in a later cleanup |
| A mark that an account number was deleted | Kept, so an old sign-in cannot bring the account back |
| Billing records, once paid plans exist | Kept for accounting and refund disputes |
| Our database backups | Up to 30 days |
| Providers' own copies | See "Who else handles your data" |
Deleting your data
In the app: Settings → Account, sync & backup → "Delete my account and data". You type DELETE to confirm. We then remove your cloud data, your sign-in account and the data on that phone.
On the web, without the app: go to https://kuaistudio.com/delete-account. Use your account ID or your email and password. For Google sign-in, email support from your Google address; we delete within 30 days. Find your account ID under Settings → Account, sync & backup. This also works if you have lost your phone or removed the app.
What we remove: your account, sign-in details, synced study data, chats, saved texts, allowance records and any feedback and screenshots you sent. The web forms delete straight away; Google email requests are handled within 30 days. Deleting your account removes our records. Providers may retain their own copies under their terms; account deletion does not erase those copies.
What we keep: the mark that your account number was deleted; daily totals with no account number; billing records, once they exist; and database backups until they expire (up to 30 days).
One thing we cannot reach: if you turned on Android backup, Android may hold a copy of Kuai's data in your Google account. Delete it in your phone's backup settings.
Children
Kuai is for adults. You must be 18 or older. The app asks you to confirm this before it uses AI features. It is not made for children and we do not knowingly collect data from anyone under 18. If you think a child has given us data, write to support@kuaistudio.com and we will delete it.
Where your data goes
Our server is on Cloudflare. The AI companies we use are in other countries. Our text and voice providers may process data internationally. Our speech recognition provider may keep data in the United States. If you live in the UK or the European Economic Area, this means your data leaves your country. We rely on each provider's data-transfer terms for this.
Your rights
In the UK and the EU you can ask us to:
- show you the data we hold about you (in the app: Settings → Account, sync & backup → Download my data);
- correct it;
- delete it;
- limit or object to how we use it;
- give it to you in a form you can move.
Our reasons for using your data are: to give you the service you asked for (account, sync, AI features); your consent (voice, usage events, feedback); and our interest in keeping the service safe and affordable (abuse checks, cost records).
If you are unhappy, write to us first. You can also complain to the UK Information Commissioner's Office (ico.org.uk).
In the US, some states give you the right to know, delete and correct your data. We do not sell your data and we do not share it for ads. To use these rights, write to support@kuaistudio.com or delete in the app.
Security
Everything between the app and our server uses HTTPS. Passwords are stored only as a salted hash. Sign-in tokens are short-lived. No system is perfectly safe. If something goes wrong with your data, we will tell you.
Changes
If we change this page in a way that matters, such as a new AI company or a new kind of data, we will tell you in the app before it takes effect. The date at the top shows when it last changed.
Contact
Kuai Studio