What is IDX, actually? 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.

The plumbing, in one paragraph

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. Technically, your website connects to the MLS data feed (modern feeds use the RESO Web API, replacing the older RETS standard), 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 “IDX integration” should actually include

The gap between good and lazy IDX is wide. The real thing includes:

• Fresh data. Feeds sync on a cadence — good implementations re-sync frequently so a listing that went pending this morning isn’t “active” on your site tonight. Ask any vendor: how often, exactly?
• Listings on your domain. Some products iframe a search portal or host it on a vendor subdomain (search.vendor.com/you). That means the search traffic, the SEO value, and often the lead itself accrue to the vendor’s domain, not yours.
• Real listing pages. Each listing should be an actual page on your site with structured data — that’s what lets your site rank for address and neighborhood searches instead of ceding them all to the portals.
• Search tools buyers expect. Map search, saved searches, filters, and listing alerts. Alerts matter doubly: they’re the reason buyers come back to your site instead of a portal.
• Behavioral capture. Every search, save, and revisit should land in your CRM as signal. IDX that doesn’t feed your follow-up system is a portal you paid for.

Compliance, briefly

MLSs enforce display rules — attribution of the listing brokerage, disclaimers, data freshness, and what fields you may show. A competent vendor handles the paperwork (each MLS has its own agreement) and keeps the display compliant so you never think about it. If a vendor waves this off, that’s a flag.

Questions that expose a weak IDX

1. Is the search on my domain, or yours?
2. How often does the feed re-sync?
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?

If you’d like the answers for your current site in writing, that’s exactly what our free audit covers — including the feed cadence and where your leads actually land.