What is IDX?

IDX is an acronym for Internet Data Exchange, which enables real estate professionals to display the most comprehensive and up-to-date property listing data on their own real estate websites.

Established by the National Association of REALTORS®, IDX is a policy under which brokers exchange permission to display one another’s listings on the internet. Broker Reciprocity is another name used for IDX, reflecting this cooperative exchange between brokers.

Although IDX is a policy, the term is commonly used to refer to the data feed of listings provided by an MLS® System. IDX also includes a set of rules for how listing data is displayed, and each MLS® System can have variations in these rules.

What is an MLS®?

MLS® is an acronym for Multiple Listing Service®, which is a proprietary database created, maintained and paid for by real estate professionals to help their clients search for, buy, and sell property. MLS® Systems are the source of IDX listing data and can serve one association or board or multiple associations or boards. An MLS® System may be owned by REALTORS®associations and/or brokers, or it may be an independent entity. The geography each MLS®System covers can range from an individual city or county to large regions.

The National Association of REALTORS® website provides more information about MLS®Systems.

How does IDX work?

Real estate board MLS® Systems make property listing data available to IDX vendors via an IDX data feed. The industry standard RETS protocol is the most common technology used to provide a data feed, although other technologies such as FTP are also used. (We no longer add new data feeds using FTP. Fewer boards continue to offer FTP, and FTP does not allow for automatically updated data as efficiently as RETS does.) IDX vendors typically download updated property data from an MLS® System several times per day, store it in a database, and make it available for search and display on their clients’ websites. Brokers are also able to get a direct IDX data feed, although they must implement a costly system for downloading, storing and displaying the data.

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