IDX — Internet Data Exchange — is the Multiple Listing Service policy that lets a real estate broker display other brokers’ listings on their own website. It is the reason a Santa Fe brokerage site can show every active listing in the county instead of only the six it has under contract.
Most brokers first meet IDX integration as a line item on a website proposal, somewhere between “responsive design” and “contact forms,” with a number next to it that seems either suspiciously small or alarmingly large. Neither reaction is wrong, because that line item can mean four completely different things. Here is what is actually behind it.
IDX is a policy first and a technology second
Before it is a feed or a plugin, IDX is a set of rules published by the National Association of REALTORS as Policy Statement 7.58 and administered by your local MLS. Two provisions matter most to a broker deciding what to build.
The first is that participation is reciprocal. A listing broker’s consent to IDX display is presumed unless that broker affirmatively tells the MLS otherwise — and a broker who refuses on a blanket basis loses the right to display anyone else’s listings. You are in the pool or you are not.
The second is that the MLS owes you data if you ask for it. On a participant’s request, the MLS must promptly provide all active listings plus a minimum of three years of sold data, and cannot carve out listings beyond the ones a broker or seller has specifically withheld. That three-year sold history is the part brokers most often forget to ask for, and it is what makes market-statistics and neighborhood pages possible later.
Access requires MLS membership and a signed IDX license agreement, broker signature included. Your developer cannot sign it for you. They connect to a feed you have licensed.
The feed is a data pipe, not a website
For most of the last two decades that pipe was RETS, the Real Estate Transaction Standard. It is on its way out. RESO retired the RETS workgroup in 2017, declared version 1.9 the final release, and stopped certifying RETS in 2018 in favor of the RESO Web API. NAR policy now requires REALTOR-operated MLSs to serve that API.
There is no national off switch, though. Each MLS sets its own RETS sunset date, so a brokerage in one market may still be running on a legacy feed while a neighboring board shut theirs off two years ago. If you are quoting a new build, ask which standard your MLS serves today and whether a retirement date has been announced. Building against a feed with a published expiration is a bill you will pay twice.
Either way, what arrives is records: price, beds, baths, square footage, photo sets, remarks, status. Every part a buyer actually sees is something you or your vendor still has to build.
Three ways listings end up on your site, and only one of them helps your SEO
Framed search. The search runs on the vendor’s server and appears inside a window on your page. It is the fastest to launch and the cheapest to license. It is also invisible to search engines, which read the frame but not what is inside it. A brokerage can display forty thousand listings this way and gain nothing in search.
Vendor subdomain. Buyers get sent to something like search.yourbrokerage.com, skinned to look like your site. Better than a frame, but the pages live on infrastructure you do not own, and the crawling and linking that accumulate over two or three years accumulate for the vendor.
Native import. The feed writes each listing into your own site as a real page with its own URL, its own markup, and its own metadata. This is the most work and the most control, and it is the only version where the listings are genuinely yours.
One caution about that third option, because it gets oversold: importing five thousand listings does not give you five thousand pages that rank. MLS remarks are byte-identical across every site displaying them, so listing pages compete with hundreds of copies of themselves. What ranks is the writing around them — neighborhood pages, market notes, buyer guides — that exists nowhere else. When I built the site for Las Campanas Realty, a Santa Fe brokerage, in collaboration with Monsoon Design, listings, neighborhoods, and agents each became their own content type fed by the Santa Fe Association of REALTORS feed, so a property page sits on the brokerage’s own domain and the neighborhood pages surrounding it are original writing no other site has.
Do I need to be a REALTOR to put MLS listings on my website?
Effectively, yes. IDX access flows through MLS participation, which means a licensed broker who is a member of the MLS signs the data license agreement; agents display listings under their broker’s participation. There is no public MLS feed you can buy access to as a marketer, a builder, or a for-sale-by-owner site. If you are not an MLS participant, your options are a syndication arrangement with a broker who is, or a site that links out to a portal instead of displaying listings itself.
What IDX integration actually costs
Three separate bills, and proposals routinely collapse them into one number.
- The MLS data license. Set by your board, and the variation is wide. MIAMI REALTORS publishes $30 a month for a broker’s own data and $100 a month for the full MLS feed. Plenty of boards charge nothing monthly but $50 to $250 to establish a feed; others add $10 to $30 a month per site.
- The connector or platform. Whatever moves data from the MLS into your site, priced monthly. A per-connection setup fee around $99 is typical.
- The build. The design, the search interface, the listing template, the filters, the maps. This is where the range is enormous, because a framed search takes an afternoon and a native listing architecture does not.
Budget the first two separately from the third in your own head, even if the proposal bundles them. The data license is a recurring cost that outlives the website, and it does not stop when the build is done.
The rules you inherit the day you switch it on
Displaying someone else’s listings comes with obligations that are easy to breach quietly. Every IDX listing must identify the listing firm along with the email address or phone number the listing participant provided, in a reasonably prominent place, in a readable color, and in a typeface no smaller than the median size used elsewhere in the listing display. Fair housing language belongs on listing pages too. Sold and withdrawn listings have to come down on the cadence your MLS specifies.
None of this is difficult. It is only dangerous when it depends on a person remembering. Build attribution and compliance language into the listing template so they are structurally impossible to omit, rather than a checklist item someone maintains by hand across a few thousand pages.
What to settle before anyone writes code
- Which standard does your MLS serve right now, and has it announced a retirement date for the older one?
- Are you licensing sold history, or only active listings? Ask for it up front even if you have no use for it yet.
- Do listing pages need to live on your domain, or is a framed search good enough for how you actually get clients?
- Who writes the neighborhood and market content that gives the listings something to rank alongside?
- If you leave this vendor in three years, what do you keep?
That last one settles more arguments than the others combined. A framed search is a rental. A native listing architecture is something you own, and the difference shows up the day you change platforms.
Patrick Iverson is a brand strategist and web developer in Santa Fe who has run an independent practice here since 2001 and has built on WordPress since 2003. If you are weighing an IDX build for a brokerage and want a straight read on which of the three approaches fits your business, the custom WordPress development page is a good place to start, or just get in touch and describe what your MLS gives you.
