IDX vs MLS: What Each One Is and What Your Website Can Show
The MLS is the database of listings brokers in your market share. IDX is the permission and feed that put the other brokers' listings on your public website.
You don’t choose between them. IDX, short for Internet Data Exchange, comes out of the MLS, the multiple listing service, through your broker’s membership, and it is how the other brokers’ listings reach a public website like yours.
| MLS | IDX | |
|---|---|---|
| What it is | The listings a market’s brokers file and share | The rule and feed that put them on members’ public websites |
| Who sees it | Its brokers and their agents, behind a login | Anyone who visits the site |
| What’s in it | Every listing filed, with agent-only fields such as showing instructions | What your MLS makes available for display, less the listings sellers keep off the internet |
| Whose it is | The broker’s membership; agents use it under the broker | The broker’s right, which the MLS may extend to agents’ own sites |
Why your IDX search shows fewer homes than the MLS
An agent who counts the homes in the MLS and then on their IDX search usually finds fewer online. Four things account for the gap:
- Sellers who opted out. A seller can tell their broker to keep the listing, or just its address, off the internet, and IDX can’t show it.
- Office exclusives. The listing is filed with the MLS but not shared with other members, so it never reaches anyone’s feed.
- Delayed marketing. The listing sits in the MLS but stays out of IDX and out of the feeds to other websites, for a period your MLS sets.
- The display’s own filters. A broker may show only some of the IDX listings, chosen by objective criteria such as area, price or property type.
So “every listing in the MLS” on a vendor’s sales page is a claim to check against your own MLS’s count.
IDX, VOW and syndication
Listings reach the public from an MLS in three ways. IDX puts them on members’ public websites and must be refreshed at least every 12 hours. A VOW, a virtual office website, shows the MLS’s listings on a member’s site only to visitors who first register as that member’s clients, and needs refreshing only every three days. Syndication is the MLS itself sending its members’ listings to other websites that advertise them.
An “MLS API” or the RESO Web API is only how the data travels. What your site can show depends on which of those licenses the feed was issued under, and a vendor who offers “full MLS access” on a public site is describing something IDX doesn’t allow.
What it means for your website
NAR’s IDX policy doesn’t require you to keep search engines away from your IDX listings. What keeps them from ranking is that each listing is the same record on every IDX site in your MLS and on the portals, and Google shows a searcher only one of them. Your site ranks for the search for a place instead: a page for each area you sell in, with the IDX listings on it, which is the work of IDX SEO. If you are choosing the product that will carry those pages, best IDX real estate websites compares the ones worth a demo.