Last updated: 24 September 2026 · Version 1.0.2 of the extension

The published policy, in seven languages, is at
https://flatin.pt/en/legal/privacidade-extensao/ — this file says the same.


The extension collects no personal data. It has no account, no analytics, no
tracking and no cookies, and it stores nothing in your browser. To calculate
IMT it sends one thing from the page to flatin.pt: the asking price.


Only on property listing pages of two sites:

• https://www.idealista.pt/imovel/…
• https://www.imovirtual.com/pt/anuncio/…

It does not run on other pages of those sites, such as search results, or on
any other site, and it has no background script. It shows the panel on sale
listings only; on rental listings it shows nothing.

1. The asking price.
2. The name of the municipality, from the page's breadcrumb or location
   block. It is used to look up the IMI rate in a table that ships inside the
   extension (src/rates.json), and it is not sent anywhere.

It uses nothing else from the page, and sends nothing else: not the address
of the page, not its title, description, photos or the seller's details. It
finds those two values in the page's own structured data and location block —
which the portal also fills with the title and the description — and takes the
price and the place name from there, ignoring the rest.


One request for each listing it shows a panel for, to
https://flatin.pt/api/v1/imt/calculate, with the price and three fixed values
that are the same for everyone: the territory (mainland Portugal), primary home
(yes) and the relief for young buyers (no). The answer — IMT, stamp duty and an
estimate for the deed — is shown in the panel. Your browser sends a CORS
preflight (OPTIONS) before it, which carries no data of its own. Both portals
are single-page websites: if the page puts another listing in front of you
without reloading, the panel is rebuilt and the request is made again for the
new price.

Nothing else is sent: not the address of the listing, not its identifier, not
the municipality. The request is made with referrerPolicy: "no-referrer", so
the address of the page is not passed in the Referer header either.

At installation Firefox says that the extension shares website content
(data_collection_permissions: websiteContent): that content is this price.


Like any request on the internet, it reaches us with your IP address and your
browser's identification string (User-Agent). The browser also names the
site the request comes from — the Origin header, for example
https://www.idealista.pt — the portal, without the path to the listing.


The application calculates the answer and does not save the price or the
result. Our server logs record, as for any visit to flatin.pt, the IP address,
the time, the address requested and the browser; they are kept for 30 days to
run the service, investigate incidents and limit abusive request rates, and
are then deleted. The request passes through the hosting and network providers
named in the flatin.pt privacy policy (https://flatin.pt/en/legal/privacidade/).
The extension adds no account, cookie or identifier that would link these
records to you.


Nothing. It does not use extension storage, page storage or cookies. Closing
the panel or the tab leaves nothing behind.


host_permissions lists the two listing-page patterns above and nothing
else. There is no permissions entry at all: no access to other sites, tabs,
browsing history or cookies, and specifically not <all_urls>.


The controller is HOLY CHAOS, UNIPESSOAL LDA (NIF 519403908, Porto,
Portugal). Contact: info@flatin.pt. flatin.pt is not a real estate agency and
holds no AMI licence.

Your rights, how to exercise them and how to complain to the supervisory
authority (CNPD) are set out in the flatin.pt privacy policy
(https://flatin.pt/en/legal/privacidade/) and on the «Your data» page
(https://flatin.pt/en/legal/os-seus-dados/).