Spanish Government Calls for Portal Algorithm Legislation

A member of Spain's ruling coalition has called for tighter regulation of the algorithms used by real estate marketplaces.

Tesh Sidi, a lawmaker representing Madrid for the left-wing Sumar alliance, has submitted a proposal to the Ministry of Housing and the Ministry of Economy, calling for stricter oversight of the data and algorithms used by portals such as Adevinta-owned Fotocasa and market leader Idealista.

Sidi's comments allege that ranked, algorithmic rental listings reduce transparency and also run the risk of distorting prices and facilitating anticompetitive behaviour.

Speaking at a press conference, Sidi alleged that Fotocasa uses "an algorithm that optimizes ad visibility using key citizen data (location, photos, price)," and warned that while such tools can improve efficiency, they can also create "a lack of transparency, bias and affect competitive equity."

The proposal, which Sidi claims was "favourably received" by the government ministries, calls for real estate portals to provide clear explanations of how their ranking algorithms function, mandatory disclosures when listings are boosted via paid promotions, and regular independent audits to ensure the technology does not discriminate against users.

Sidi's call for regulation comes amid soaring rents across Spanish cities, with landlords facing restrictions on rent increases under current government policies. Annual rent hikes are capped at 2.2% for 2025, below the current inflation rate of 3.0%.

Idealista has responded to the proposal, saying its algorithmic ranking system is already transparent. In a post on X (formerly Twitter), the company said, "This information, as all our users know, is public and visible from the results page."

Idealista's 'How we sort search results' page says:

"When you do a search, we show you results sorted by default according to relevance criteria" [translated from Spanish]. Listing metrics include publication date, quality and completeness of the listing, and whether the client paid for more visible listings.