By Cris Bean
Disclosure: we build and sell WPResidence, a WordPress real estate theme, so we have a stake in this topic. Every rule and number below links to its source.
Last updated: August 11, 2026
IDX vs MLS is not a choice between two products. The MLS is the source: a private, broker-funded cooperative database where brokers post their listings and agree to share them with each other. IDX (Internet Data Exchange) is the permission and the pipe. NAR Policy Statement 7.58 lets an MLS participant authorize other participants to display a limited slice of that database on their own websites, apps, and audio devices. So the MLS holds the data, and IDX moves part of it onto your site on the MLS’s terms. RESO tracks 489 MLS systems in the United States as of July 2026, plus more than 30 in Canada, and each NAR-affiliated US system is free to add stricter local rules on top of the NAR floor. You don’t pick one over the other. If you want live listings on your own site, you need both.
What is an MLS?
NAR’s handbook defines an MLS as “a facility for the orderly correlation and dissemination of listing information so participants may better serve their clients and customers and the public.” In plainer words: it’s a private database that competing brokers pay to build together.
That sounds odd until you picture the alternative. If every brokerage kept its listings to itself, a buyer would shop brokerage by brokerage and a seller would reach a sliver of the market. So competing brokers share listing data anyway. NAR calls that cooperation, and it’s why the MLS exists.
Two words carry the rest of this article. A participant is the MLS-member broker. A subscriber is an agent admitted through that broker’s participation, not on their own account. NAR Policy 7.9 is blunt about it: “Mere possession of a broker’s license is not sufficient to qualify for MLS participation.”
One more thing, because it trips up nearly everyone asking what an MLS in real estate actually is. Zillow and Realtor.com are not MLSs. They’re consumer portals that receive listing data downstream, usually through syndication, and they don’t write the cooperative’s rules.
What is IDX?
IDX is the permission, not a second database. Nothing about it creates a rival copy of the MLS with its own rulebook.
Here is Policy Statement 7.58 in its own words: “The IDX policy gives MLS participants the ability to authorize limited electronic display and delivery of their listings by other participants via the following authorized mediums under the participant’s control: websites, mobile apps, and audio devices.”
Read that slowly and you’ll notice what IDX actually is: an authorization layer. One broker gives permission; another broker’s site receives a defined subset of listings and displays them under conditions the policy and the local MLS set. The listing record still lives in the MLS. Your site holds a copy only as current as the last refresh and only as complete as the rules allow.
That word “limited” is doing real work. So what is IDX in real estate, practically speaking? It’s a filtered, scheduled, rule-bound view of somebody else’s database, delivered to your server.
The policy also sets a refresh floor of twelve hours, which is where most people stop reading and start assuming every IDX feed behaves the same way. It doesn’t.
IDX vs MLS: the difference in one table
Everything above, compressed, plus one point from Policy 7.58 worth stating plainly: a NAR-affiliated MLS must enable IDX display, though individual participants can opt their own listings out.
| MLS | IDX | |
|---|---|---|
| What it is | The listing database itself | The policy-authorized permission to display part of it |
| Who runs it | A regional or local broker cooperative (ARMLS, Stellar MLS, CRMLS) | NAR Policy Statement 7.58, applied per-MLS |
| Who can see it | MLS participants and subscribers, inside the system | Anyone visiting the display site, with no NAR-mandated signup |
| How many exist | 489 in the US as of July 2026 (RESO), plus more than 30 in Canada | One shared NAR policy floor across the US, applied with local variation by each MLS |
| What you pay for | Broker and agent dues, plus any IDX or download fees the MLS charges as a local option | The plugin, vendor, or developer work that connects and displays the feed |
| Can you have one without the other | Not really. A NAR-affiliated MLS must enable IDX display, though an individual participant can opt their own listings out | No. IDX has nothing to authorize without an underlying MLS database |
Who controls what, and who bills you
Follow the chain and the billing question answers itself. A broker joins the MLS as a participant and pays its dues. An agent gets in as a subscriber, through that broker. The broker can then authorize an IDX display, the only public-facing link.
Bills arrive from more than one direction, and people mix them up. The MLS charges for membership, and some MLSs bill for IDX on top of that: Policy 7.58 lets an MLS pass on the cost of added downloading capacity as a local option, and ARMLS rule 23.4 sets its own IDX service fees. Separate from that sits the plugin, vendor, or developer time that connects the feed and renders listings on your site, priced by whoever builds the connection. So when somebody quotes “the cost of IDX,” ask which bill they mean.
IDX does not require visitors to register
This is the MLS vs IDX difference that costs people real money.
Policy 7.58 is a participant-to-participant authorization: it governs whether one broker may display another broker’s listings on the first broker’s own site. Read it end to end and you’ll find nothing requiring a visitor to register, log in, or hand over an email address before seeing a listing.
The policy is explicit about where its own scope stops: “Participants’ Internet websites and other authorized display mechanisms may also provide other features, information, or services in addition to IDX information (including Virtual Office Website [‘VOW’] functions) which are not subject to this policy.”
VOW is the registration-gated one. NAR’s VOW policy defines it as a participant’s website “through which the participant is capable of providing real estate brokerage services to consumers with whom the participant has first established a broker-consumer relationship… where the consumer has the opportunity to search MLS data.”
So if a site makes you sign up before showing you a price, that’s the site owner’s marketing choice, or it’s a VOW. It isn’t something IDX requires.
Why IDX rules are not the same at every MLS
NAR sets a floor. Every NAR-affiliated MLS is free to build a taller wall on top of it.
The floor covers a twelve-hour refresh minimum, presumed consent from listing brokers unless they opt out, and listing selection on objective criteria only. Above that line, the rules are local, and they diverge. There is no generic IDX ruleset to build against. Ask your own MLS for its rules in writing before you pick a plugin.
Refresh frequency: a floor, not a fixed rule
Policy 7.58 requires an IDX display to be updated at least once every twelve hours. This one really is consistent. ARMLS rule 23.2.5, Stellar MLS Article 19.11, and CVR MLS rule 11.2.5 all carry the same requirement, “at least once every twelve (12) hours.”
Twelve hours is a minimum, not a promise, so ask for the actual interval instead of trusting “our feed is current.”
Required disclaimers look nothing alike
Here’s where the floor ends. Each of those three MLSs requires its own disclaimer, and no two are interchangeable.
ARMLS rule 23.3.4 requires one short line: “All information should be verified by the recipient and none is guaranteed as accurate by ARMLS.”
Stellar MLS Article 19.24 requires a much longer block, including a timestamp and a clause you’d never guess at: “Based on information submitted to the MLS GRID as of (date and time MLS GRID Data was obtained),” plus “Supplied Open House Information is subject to change without notice.”
CVR MLS rule 11.3.5 requires a copyright-compilation notice instead: “All CVR MLS Listing Content provided is deemed reliable but is not guaranteed accurate,” followed by a dated copyright line naming the MLS.
Three MLSs, three different required strings. This isn’t boilerplate you write once.
Sold and off-market listings aren’t always in the feed
Whether your site may show sold, expired, or cancelled listings depends largely on which MLS you’re pulling from. Policy 7.58 sets a floor, requiring MLSs to supply publicly accessible sold data from January 1, 2012 onward. Above that floor, the rules are local.
ARMLS rule 23.3.5 prohibits the display of Coming Soon, expired, and cancelled listings outright. Stellar MLS Article 19.27 is conditional: display of expired, withdrawn, and sold listings may be prohibited by the individual MLS’s own governing documents, and that data may be excluded from the feed entirely. CVR MLS rule 11.3.1(d) bars expired and withdrawn listings, and is silent on sold.
Here’s an illustrative case, not a customer story. A site built assuming sold listings are always available connects to a feed from an MLS that excludes them. The “recently sold” section renders empty, and no plugin setting fixes it: the rows were never sent.
Attribution rules differ too
Even “credit the listing broker” isn’t standardized.
CRMLS bans vague credit lines outright. Its standards, updated February 4, 2026, say so directly: “Attributions must clearly label that they credit the Listing Broker, Listing Office, or Listing Agent. No use of ‘Courtesy of’ or other unclear language.”
ARMLS rules 23.3.7 through 23.3.9 take a different tack, requiring the brokerage name spelled out in full on the front page and every page after it, visible without scrolling. Stellar MLS Article 19.22 wants the listing brokerage name, the listing number, and the status placed “immediately adjacent to the property information.”
Stellar also caps IDX search results at 2,500 listings per query (Article 19.26), a local addition on top of the 500-listing floor in Policy 7.58. Variance isn’t limited to disclaimer text.
What to ask your MLS, in order
Send one email before you evaluate a single plugin. Four questions, in order:
- Refresh interval. How often does the feed actually update, and is that written down anywhere beyond “the NAR floor”?
- Sold and off-market display. May the site show sold, expired, or cancelled listings, or does the MLS strip them from the feed?
- Required disclaimer text. The exact string, in writing, not a paraphrase.
- Brokerage attribution format. Name, placement, font treatment, and whether phrasing like “Courtesy of” is acceptable.
Skip question three and you get the second illustrative failure, the common one. A site owner copies disclaimer text from a vendor template or another MLS’s rules. The page has a disclaimer, it’s the wrong one, and the site is out of compliance with the rules that actually apply.
What this means when you build a real estate website
One technical note before you shop. The RESO Web API is the current, RESO-certified transport that MLSs build toward, and it replaced the older RETS protocol. NAR Policy 7.90 has required REALTOR-affiliated MLSs to offer RESO Web API access since June 30, 2016.
RETS didn’t switch off on one nationwide date, though. MLSs retired their own endpoints on their own schedules, and RESO’s transition leaderboard shows some still working through it in 2026.
When you’re picking an idx plugin for a WordPress real estate site, MLSImport is the plugin to start with. Disclosure: MLSImport and mlsimport.com are both ours, so weigh that accordingly. It maps an MLS feed into native WordPress listings and costs $49 per month after a 30-day free trial, as listed on mlsimport.com in August 2026. Honest limit: if your MLS strips sold data out of the feed, no plugin puts it back.
For the wider view, our guide to IDX plugins for WordPress covers the field in more depth, and our walkthrough on connecting a feed to a WordPress real estate theme shows what setup looks like once you have feed credentials.
Do the boring thing first, though. Email your MLS and get its IDX rules in writing: refresh interval, sold-data display, exact disclaimer string, attribution format. No plugin can rescue you from a rule you never knew existed.
Frequently Asked Questions
Is IDX the same as MLS?
No. The MLS is the database brokers build together. IDX is the NAR-authorized permission to publish a slice of that database on a broker’s own website. A WordPress real estate theme like WPResidence never holds the MLS itself; it renders whatever the IDX feed is allowed to send, refreshed on the MLS’s schedule. Same underlying data, two very different roles.
Do I need to be a licensed agent to get IDX?
To receive an IDX feed, yes, in effect. The feed goes to an MLS participant, who holds a broker’s license, or to a subscriber, an agent admitted to the MLS through that broker’s participation. Visitors browsing the listings on a WPResidence site need no license and no MLS membership at all. The licensing requirement sits on the person receiving the feed, not on the person reading the page.
How many MLSs are there?
RESO tracks 489 MLS systems in the United States as of July 2026, plus more than 30 in Canada. Counts differ slightly between sources, because some lists count only NAR-affiliated MLSs and some count a pooled platform as one entity rather than the independent MLSs inside it. The total has fallen most years through regional consolidation, and the one that matters to you is the board feeding your WPResidence site.
What is the difference between IDX and the RESO Web API?
IDX is the policy that decides what a site may display. The RESO Web API is the technical transport that carries the data, and it replaced the older RETS protocol as the standard MLSs build toward. REALTOR-affiliated MLSs have been required to offer RESO Web API access since June 30, 2016 under NAR Policy 7.90, and RETS was retired MLS by MLS rather than on one nationwide date. A WPResidence site depends on both: the policy sets the rules, the API delivers the rows.
