This article is part of our Real Estate & Property Management Marketing Guide: how buyers, sellers, owners and tenants find you online, what the housing ad rules allow, and how to choose the right help. Want to know where your site stands? Get a free 20–30 page website audit within 24 hours.
IDX is the system that lets you show other brokers' MLS listings on your own website. It stands for Internet Data Exchange. Under NAR's policy, it lets MLS participants allow limited electronic display of their listings by other participants, so a buyer can search the whole market on your site instead of leaving for a portal.
IDX sounds technical, but the decisions behind it are business decisions. Who supplies the feed? Who owns the search pages? Can Google read them? This guide explains the moving parts in plain English, so you can ask better questions before you pick a website or IDX vendor.
It is part of our Real Estate and Property Management Marketing Guide, which covers everything from your first agent site to a full brokerage marketing plan.
Key Takeaways
- IDX is a permission system run through your MLS: listing brokers agree to let other participants display their listings, within MLS rules.
- A VOW (virtual office website) is different: it serves registered consumers you already have a broker-consumer relationship with, not the general public.
- RETS is the old way MLS data moved between systems; RESO says it is deprecated, and the RESO Web API is the current standard.
- Your MLS, not your web designer, sets the display rules, so read your local IDX rules before launch.
- How your IDX pages are built (framed, subdomain or on your own domain) affects what search engines can see and credit to you.
What IDX actually is
Think of your MLS as a shared database. Every participating broker adds listings to it. IDX is the agreement that lets each participant pull a copy of that data and show it to the public on a site they control.
A few points follow from that:
- Access comes through the MLS. RESO, the standards body, notes that access to data from the Web API is gained through local MLSs, after you agree to that MLS's data use and licensing policies.
- It is limited display. You show listings under rules set by your MLS. You do not get to edit another broker's listing or present it as yours.
- Sellers have choices. NAR's policy page on Multiple Listing Options for Sellers explains that a seller can opt out of IDX, or, since 2025, choose a "delayed marketing" listing that is kept out of IDX and syndication for a period the local MLS allows.
That last point matters for your site. Not every MLS listing will appear in your IDX search, and that is by design.
IDX vs VOW: two ways to show MLS data
Agents often hear "IDX" and "VOW" used as if they mean the same thing. They don't.
| IDX | VOW | |
|---|---|---|
| Who sees it | The public | Registered consumers you already work with |
| Purpose | Advertising listings | Providing brokerage services online |
| Sign-up needed | Usually optional (your choice for lead capture) | Yes, registration and terms of use |
| Typical use | Public home search on an agent site | Client portal with deeper MLS data |
North Carolina's real estate commission described the VOW model when NAR adopted it: consumers register with a name and email address and agree to terms of use before they can search, and registration alone does not create an agency agreement. NAR's current guidance on delayed marketing listings repeats the core idea: VOW display is not for advertisement but helps provide brokerage services to consumers with an established broker-consumer relationship.
For most individual agents, a public IDX search is the starting point. A VOW makes more sense when you want a logged-in client area and your MLS and state rules support it.
RETS vs the RESO Web API: how the data moves
IDX is the permission. A data transport standard is the pipe. There have been two main pipes.
RETS (the old pipe)
RETS stands for Real Estate Transaction Standard. RESO describes it as an older standard that is proprietary to the real estate industry, and says it has been deprecated and is no longer supported by RESO. Its certification page adds that RESO discontinued certifying RETS in 2018.
RESO Web API (the current pipe)
The RESO Web API is built on common web technology, so developers outside real estate can work with it. According to RESO's certification page (checked 29 October 2026), at least 90% of MLSs have RESO-certified Web API services, and NAR MLS policy requires compliance with RESO's most recent standards.
The Data Dictionary (the shared vocabulary)
The pipe is only half the story. RESO's Data Dictionary defines fields and pick lists so that "pool features" or "fencing" mean the same thing from one system to the next. When your vendor says it is "RESO certified," ask whether that covers the Web API, the Data Dictionary, or both.
What this means for you: if a vendor still builds new sites on a RETS feed, ask why. It may still work with your MLS today, but RESO has moved on.
The rules that apply to your IDX pages
Your MLS publishes its own IDX rules, based on NAR's model, and many of the details are in member-only documents. So treat this section as a list of questions to check with your MLS and broker, not a rulebook.
Who listed it. NAR's Code of Ethics says REALTORS® must not present content developed by others without either attribution or without permission (Standard of Practice 12-10). Your MLS will also have its own listing-firm display rule.
Keep it current. The same Code says REALTORS® shall use reasonable efforts to ensure that information on their websites is current (Standard of Practice 12-8). Stale "active" listings are a compliance problem and a trust problem.
Your firm name and license. Standard of Practice 12-9 requires agent websites to disclose the firm's name and the agent's state of licensure. State rules may add more. See agent website vs brokerage site for a California example.
Compensation. Since the NAR settlement, offers of compensation can't appear on the MLS. NAR's settlement FAQ says a listing broker may add offers of compensation to an IDX or VOW display only for listings of their own brokerage (FAQ 53). Our NAR settlement and your website article covers this in more detail.
Fair housing. IDX search filters and the copy around them are advertising. Read Fair Housing advertising rules for real estate websites before you write neighborhood blurbs.
Rules vary by MLS and state, so confirm with your MLS and your broker of record before you launch.
How IDX setup affects your SEO
Here is where IDX choices stop being purely technical. Three common setups:
- Framed or embedded search. The vendor's search runs inside a frame on your page. It is quick to set up. The listing pages live on the vendor's system, so your own domain may get little search credit for them.
- Vendor subdomain. Listings live on something like search.yourdomain.com, hosted by the vendor. Better than a frame for branding, but you depend on the vendor's templates and page speed.
- Listings on your own domain. The data comes through an API and your site renders listing and search pages itself. This takes more work, and gives you the most control over speed, page structure and internal links.
No setup will make a site rank on its own. Thousands of sites show the same MLS data, so listing pages alone rarely set you apart. What usually does is the original content around them: neighborhood guides, market notes and clear agent pages. Our guide to neighborhood and community pages shows how to do that without creating thin doorway pages.
Structured data can help search engines and AI tools understand who you are. Schema.org has a RealEstateAgent type for your business entity, and our post on schema markup for real estate websites walks through the options.
Questions to ask an IDX vendor
- Do you use the RESO Web API with my MLS, or RETS?
- Are listing pages on my domain, a subdomain, or in a frame?
- How often does the feed refresh, and how are sold or withdrawn listings removed?
- Who owns the leads and the contact data if I leave?
- Can I add my own content to search pages for specific areas?
- How do you handle my MLS's display and disclaimer rules?
If you want to compare builders, our roundup of IDX WordPress developers is a starting point.
Next step
Once you understand IDX, the next question is what else your site needs around it. Read Real Estate Agent Website Must-Haves for the full checklist. Or get a free 20–30 page website audit within 24 hours to see how your current IDX setup looks to search engines.
Frequently asked questions
Do I need my broker's permission to add IDX to my agent website?
In most markets, yes. IDX access runs through the MLS, and the MLS participant is usually your broker. Your MLS will tell you what paperwork it needs and whether agents can get a feed directly or only through the brokerage.
Why don't all MLS listings show up in my IDX search?
Sellers can opt out of IDX, and since NAR's 2025 policy they can also choose a delayed marketing listing that stays out of IDX and syndication for a period set by the local MLS. Office exclusive listings are not shared with other participants at all.
Is RETS still allowed?
Some systems still use it, but RESO calls RETS deprecated and stopped certifying it in 2018. If you are building a new site, ask your vendor to use the RESO Web API where your MLS offers it.
Will IDX listings help my website rank?
They can help visitors, but the same listings appear on many sites. Rankings usually depend more on your original local content, your Google Business Profile and how well your site is built. Treat IDX as a feature, not an SEO strategy.
What is the difference between IDX and syndication?
IDX lets other MLS participants display listings on their own sites. Syndication generally means sending listings to third-party portals. Both are controlled by MLS rules and seller choices, and a delayed marketing listing is kept out of both during the delay period.
