What is IDX? MLS integration explained without the jargon

Every real estate website vendor says “IDX integration included.” Few agents ever get a straight explanation of what that means, which makes it hard to know whether you’re buying the real thing or a widget. Here’s the plain version.

What is IDX, in plain terms?

IDX is permission plus plumbing: the MLS rule that lets you show other brokers’ listings, and the data feed that puts them on your site.

Your MLS is the database where brokers share listings. IDX (Internet Data Exchange) is the set of MLS rules that lets member agents display each other’s listings on their own websites. NAR’s model IDX policy (Handbook on Multiple Listing Policy, 2026 edition) describes it as giving MLS participants “the ability to authorize limited electronic display and delivery of their listings by other participants” on websites, mobile apps and audio devices they control.

Technically, your website connects to the MLS data feed, pulls listing data and photos on a schedule, and displays them under your brand, subject to your MLS’s display rules. That’s IDX: other agents’ listings, legally on your site, refreshed automatically.

What do IDX, MLS, RETS and RESO mean?

They’re four layers of the same system: the database, the permission, the old pipe and the new pipe.

How do listings get from the MLS to your website?

Through an approved data feed that your vendor connects to and refreshes on a schedule. The steps are the same almost everywhere:

1. Your broker authorizes it. IDX access runs through your brokerage’s MLS participation, and each MLS has its own agreement to sign.
2. The vendor connects to the feed. A modern vendor uses the RESO Web API to pull listing data and photos.
3. Listings are displayed on your site. The vendor builds search, maps and listing pages from the data, under your brand.
4. The feed refreshes. NAR’s policy requires participants to refresh MLS downloads and the displays they feed “not less frequently than every 12 hours.” Many MLSs and vendors go much faster.
5. Status changes flow through. When a listing goes pending, sells or is withdrawn, the next sync updates or removes it.

What do the MLS display rules require?

Attribution, freshness and accuracy, plus whatever your local MLS adds. NAR’s model IDX policy includes these, among others:

• Credit the listing firm. Displays must identify the listing firm and the email or phone number the listing broker provides “in a reasonably prominent location,” in type no smaller than the median used for listing data.
• Refresh at least every 12 hours. Stale data is the thing these rules exist to prevent.
• Don’t edit other brokers’ listings. Participants “shall not modify or manipulate information relating to other participants’ listings.”
• Respect opt-outs. Listing brokers can refuse IDX display, either for all their listings or one at a time, so some listings may not appear on any IDX site.

Each MLS adopts its own version of these rules and can add requirements, such as disclaimers or limits on which fields you may show. A competent vendor handles the paperwork and keeps your display compliant so you never think about it. If a vendor waves this off, that’s a flag. This is a summary, not legal advice; your broker and your MLS have the final word on what applies to you.

What should good IDX integration include?

Fresh data, pages on your own domain, and a connection to your CRM. The gap between good and lazy IDX is wide.

Two of those rows deserve more explanation.

Listings on your domain. When search runs in an iframe or on a vendor subdomain, the search traffic, the SEO value, and often the lead itself accrue to the vendor’s domain, not yours.

Behavioral capture. Every search, save, and revisit should land in your CRM as signal. Listing alerts matter twice over: they’re the reason buyers come back to your site instead of a portal, and each return visit tells you something. IDX that doesn’t feed your follow-up system is a portal you paid for. We’ve written more about treating the website as part of your business system.

Does IDX help your website rank?

A little, directly, and more through the pages you build around it. Listing pages are useful, but they’re rarely what ranks.

An IDX listing page carries the same MLS description and photos as the same listing on every other IDX site and portal in your market. Search engines generally show one version of near-identical content, and it tends to be the site with more authority, which is often a portal.

What you can rank for are the pages nobody else has: neighborhood and area pages with real local knowledge and the current inventory embedded. IDX makes those pages useful, because the listings on them are live. We go through the details in why agent websites don’t rank.

What should you ask an IDX vendor?

Seven questions will tell you most of what you need to know about a vendor’s IDX:

1. Is the search on my domain, or yours?
2. How often does the feed re-sync, exactly?
3. Do listings have their own indexed pages with structured data?
4. Where do saved searches and favorites go: my CRM, or your database?
5. Who files and maintains the MLS paperwork?
6. Are MLS or feed fees included, or billed separately?
7. If I leave, do I keep the domain, the contacts and the pages?

Ask for the answers in writing. A vendor with good IDX will be glad to give them. Our 2026 guide to real estate website platforms notes how the major vendors handle IDX, if you want a starting point. To see what those answers usually cost, our 2026 breakdown of agent website prices lists published figures.

Where to go from here

Every Broker & Agent website includes full IDX search on your own domain, with listing pages, maps, filters and saved homes. If you’d like to see the answers running on a site of your own, that’s exactly what our free website preview covers, including the feed cadence and where your leads actually land.