Privacy policy

Bytky is a property-market tool for Czechia: a website, a public API and a browser extension that add history and context to listings on Sreality.cz and Bezrealitky.cz. Bytky is not affiliated with either site.

The controller of your personal data is Douglas Anthony Silkstone, Nademlejnská 600/1, Hloubětín, 198 00 Praha 9, Czech Republic (IČO 10911243). You can reach us about privacy at hello@bytky.com, or through the data box (datová schránka) uebsrdr.

Bytky reads the public listings both sites publish and keeps a history of how each one changes. This is market data about properties, not about people.

What we keep

Price and currency, service and utility charges, size, layout, floor, condition, status, the address and map location, the number of photos, view and contact counters, and when each of these changed.

Who advertises

Only whether the advertiser is a private person, an agency or a developer, and for agencies and developers their public business profile: name, logo, website, company id (IČO), office address, and their legal form from the public ARES business register. For sole traders, Bytky shows only the trading name.

What we never keep

Advertisers' personal details: the names, phone numbers, email addresses and profile pictures of private sellers, landlords and brokers. They are removed before anything is stored.

Descriptions

We don't republish listing descriptions. We keep a fingerprint of the text to notice when it changes.

Every listing page on Bytky links back to the original advert, where the advertiser's own details remain under the source site's control.

To learn which features help people find a home, Bytky measures how it is used with PostHog, an analytics service, on its EU cloud in Frankfurt. Everyone is counted anonymously and without cookies. Only if you say yes is your use linked to your account.

Everyone

The pages you open, the buttons and links you click (their text, never anything you type), the page that sent you, your browser and device type, page load times, and errors the site runs into. Nothing is stored in your browser: PostHog turns your IP address and browser into a hash with a secret that changes every day and is then deleted, so visits can't be linked from one day to the next. Our servers also count product events (signing up, saving a listing, an alert sent) with a random id for each, so they can't be linked to you or to each other.

If you opt in

When you tick “Help improve Bytky” at sign-up, answer yes to the question we ask once after you sign in, or switch it on in Settings, the same events are linked to your account's internal id, never your name or email address. PostHog then keeps a profile under that id (whether the account is ours, when it was created) and an id in your browser's cookies and local storage, and may record your sessions on the website: a replay of the pages as you saw them, with everything you type and every name, email address and phone number hidden.

The extension

Sends usage statistics only if you switch them on, in the extension's settings or, while signed in, by opting in for your account. Then it reports which of its features you use, its version, your browser and its language. Never the listings you look at, their addresses or your saved-search filters.

How it travels

Your browser and the extension send these through api.bytky.com, which passes them on to PostHog with your IP address. PostHog works out your country and city from it, then drops the IP address; it is not stored. Bytky strips sign-in tokens, codes and email addresses from page addresses before they are sent.

Where it's stored

PostHog's EU cloud (Frankfurt, Germany).

Changing your mind

Switch it off or on any time in Settings → Your data → Usage analytics, or in the extension's settings. Off, you're counted anonymously again from that moment.

How long

Kept under PostHog's retention settings. When you delete your account we ask PostHog to delete your profile and the events and recordings linked to it; that happens within days. Anonymous counts can't be linked to you, so they stay.

Photos are shown by linking to the source sites. When you look at a listing on Bytky, your browser loads its photos directly from Sreality's or Bezrealitky's image servers, and the gallery credits and links the source. Bytky never downloads, copies, resizes or stores the photos themselves.

To recognise the same flat advertised on both sites, Bytky briefly reads up to three photos of some listings and keeps only a short numeric fingerprint (64 bits) of each. The image is discarded straight away; the fingerprint can't be turned back into a picture.

Because photos load from the source sites, those sites receive the usual request from your browser (your IP address and browser details), as they would if you visited them.

You can use the map and listing pages without an account. If you create one, we keep:

Profile

Your name and email address, and whether the address is verified.

Sign-in

Your password as a one-way hash (never the password itself), a linked Google account if you choose one, and your active sessions with the IP address and browser they started from.

What you save

Watchlists with your notes, saved searches with their filters, and the alerts we raise for them.

Preferences

Display currency and language, which extension panels and badges you show, and how alerts reach you.

Analytics choice

Whether you opted in to usage analytics linked to your account, and when you last changed it.

Bytky news

Whether you want our monthly email, and each answer you gave: when, where in Bytky, and the wording you said yes to. We send it only with your consent, and that record shows it.

Households

The households you belong to, your role in each, and invitations you send (with the invitee's email address) or receive.

Earlier emails

Until 14 October 2026, when email delivery was switched on, a copy of each email we sent you (sign-in links, verifications, invitations, alerts) was kept in our database instead of being delivered. Those copies are deleted with your account; emails sent since then are not stored.

We use this only to run Bytky for you: to sign you in, keep your lists, share them with your household and send the alerts you asked for. We don't sell it, profile you or show you ads.

Contacting an agent. “Contact the agent” writes an enquiry from your renter profile in your browser. The extension puts it into Sreality's or Bezrealitky's own contact form or chat (without the extension you copy it), and you press send there: the message goes straight to that site, never through Bytky, and Bytky never sends anything for you. If you're signed in, the extension notes that you contacted the agent about a listing (when, and how many times). That record is in your data export and is deleted with your account.

Feedback. What you write in the feedback form or the extension's uninstall survey is stored with the extension's version and your browser family (Chrome, Edge, Firefox) when they're known, never your IP address. Sent while you're signed in, it is linked to your account, included in your data export and deleted with your account; otherwise it is anonymous.

• It runs only on Sreality and Bezrealitky pages. It reads the listing identifiers on the page to look up Bytky's data for them, and nothing else about your browsing.
• Your settings are kept in your browser. If you sign in, the extension stores a sign-in token in the extension's own storage and syncs your settings with your account.
• While you're signed in it checks for new alerts every 10 minutes to show browser notifications, which you can switch off in Settings.
• To ask for a store review only after real use, it counts in your browser how many listings and on how many days you've used it. That count never leaves your browser. When you remove the extension, your browser opens a short, optional survey whose address carries only the extension's version. That page is measured like the rest of the website.
• It sends usage statistics only if you switch them on (see How we measure usage); otherwise it sends none.

Bytky sets one cookie of its own, the sign-in session cookie, and only once you sign in. Your light or dark theme choice is kept in your browser's local storage. There are no advertising cookies. Analytics use no cookies or storage at all unless you opt in; then PostHog keeps an id for your browser in a cookie and local storage (named ph_…), removed again when you switch it off or sign out (see How we measure usage).

Some services see requests from your browser or handle data for us:

• Our hosting provider (Railway) runs Bytky's servers and database.
• PostHog (EU cloud, Frankfurt) receives the usage measurements described above. Your browser and the extension send them through api.bytky.com, which passes them on.
• OpenFreeMap serves the map tiles your browser loads on the explorer.
• Sreality and Bezrealitky serve the listing photos your browser loads.
• Cloudflare delivers the emails we send you (sign-in links, confirmations, invitations and alerts) and receives the emails you send to our addresses.
• Loops sends Bytky news, only if you said yes: it gets your email address, first name and language, and tells us when you unsubscribe in one of its emails. Saying no or deleting your account removes you from its list.
• Google, only if you choose to sign in with a Google account.

• Account data is kept for as long as you have an account and deleted when you delete it.
• Sessions end when you sign out and expire after 30 days without use.
• Sign-in, verification and reset links expire within an hour (sign-in links after 15 minutes).
• Household invitations expire after 7 days.
• Usage measurements are kept under PostHog's retention settings; those linked to your account are deleted with it (see How we measure usage).
• Listing history is kept as long-term market data. It contains no personal data about advertisers.

Under the GDPR you can access, correct, export and delete your personal data, and object to how we use it. Most of this is self-service in Settings:

Export

Settings → Your data → Download my data gives you a zip of JSON files with everything your account holds. Passwords and sign-in tokens are never included.

Correct

Change your name, email address and password in Settings → Profile.

Delete

Settings → Your data → Delete account removes your account at once: your profile, sign-in methods, every session (you're signed out everywhere, including the extension), watchlists, saved searches, alerts, settings, invitations, the emails we sent you and feedback you sent while signed in. We then ask PostHog to delete the usage events and recordings linked to your account; that happens within days.

Households

When you delete your account or leave a household you share, the household continues: if you were its only owner, its longest-standing admin (or member) becomes the owner, and listings you added stay without your name. A household where you were the only member is deleted with its shared lists.

You can also complain to the Czech data protection authority, the Úřad pro ochranu osobních údajů (uoou.gov.cz).

If we change how Bytky handles personal data, we'll update this page and its date. If a change affects your account in a meaningful way, we'll tell you by email first.