What are IDX, MLS, RETS and RESO API

Nowadays, building a professional real estate website is the natural part. Populating it quickly with different listings or importing them is the real challenge web developers and realtors have to face.

If you’re a real estate agent, a freelancer, or an agency, you might have trouble importing listings quickly to your client’s website.

This is where IDX, MLS, RETS, and RESO concepts step in to help make this easy.

Let’s take a look at what they are and how they can help you finish your real estate web projects quickly and under budget.

What is IDX?

IDX, or Internet Data Exchange, is not a real estate-focused technology but a set of rules and agreements between different brokerages in a particular area.

The Internet Data Exchange agreement stipulates how individual real estate listings can be shared online with different real estate listings.

IDX controls how the data is organized and shared, and, more importantly, it sets which listings are available.

That being said, brokerages can set their own rules for IDX – with some not participating in the agreement at all and not displaying their listings on other websites.

Other brokerages may decide to share only specific properties or listings and keep others hidden, but the majority of brokerages will choose to display all their available listings for IDX.

A local MLS or Multiple Listing Service will set the overall IDX policy. The MLS also acts as a governing body for multiple real estate associations in a particular area.

Be sure to read the article ‘What Is IDX (Internet Data Exchange) – The Complete Guide‘ for in-depth insights.

MLS – Multiple Listing Service

The Multiple Listing Service, or MLS, for short, is a set of services that allows different local real estate brokerages to share information, cooperate, and provide potential buyers with information on the available listings in their area.

Multiple Listing Services have been around for hundreds of years, and their ultimate goal is to offer potential clients more in terms of available listings.

When a real estate brokerage makes a sale with the help of another brokerage that is part of the same MLS, the resulting profit splits among them, usually in the form of a commission.

It’s important to note that each MLS has a different IDX policy set for its real estate broker members.

Since there are over 700 MLSs in the US, and each has its internal policy, take some time and review the terms & conditions in which your local MLS shares real estate listings.

It will help you build a website with real estate listings you are allowed to share on your website without risking any infringement.

Take a moment to read the article “What is Multiple Listing Service (MLS) in Real Estate and How Does It Work” for a clear understanding.

What are IDX, MLS, RETS and RESO API

IDX Integration Solutions

Some companies offer IDX integration solutions, most often in the form of a 3rd party plugin, iframe, or widget that you can embed on your website.

Another way to integrate IDX into your website is through a URL that can be sent directly to users or a UI, which allows the users to search for listings directly.

Traditional IDX Advantages include:

  1. Implementing a conventional IDX solution on your website is quite expensive, but you can do it within a reasonable amount of time.
  2. Some solutions also offer customization options but cost extra money, and it’s a service you can buy with difficulty.
  3. Listings display directly from the MLS without being imported into your database, along with the search tools necessary to view listing photos, add listings to favorites, and other features.

Traditional IDX Disadvantages include:

  1. Other real estate brokerage websites will have the same search and user interface as you since IDX providers generally offer very little in terms of customization.
  2. SEO optimization is quite limited, mainly if the system uses an iframe for the listings. Search engines cannot index the listings from within iframes, meaning that your client will have very little traffic from search engines.
  3. Since you will be using the user interface provided by your IDX solution, it will be inconsistent in terms of design, resulting in a web page that is botched together from different elements.
  4. Responsive design may be limited or inexistent – since you cannot fully control the IDX user interface, your website may not be fully responsive. Make sure that the solution you opt for is fully responsive since most sites get visits from mobile devices.
  5. High costs.

Real Estate Transaction Service – RETS API

With RETS or Real Estate Transaction Service, you will be able to write your code that imports real estate listings directly to your client’s website database.  See also how RESO API and RETS feed are different.

RETS API advantages:

  1. The most significant advantage of using RETS is that you have better control over the look and design of the listings.
  2. With RETS, the listings are also SEO-friendly and fully responsive.
  3. RETS uses DMQL, a query language, to search for photos, properties, and other types of data available on the MLS.

RETS API disadvantages:

  1. You need to code the import tool, which costs a lot of money to buy as a service.
  2. High Costs to create and maintain.
  3. RETS only standardizes how to connect and query the data, but the fields are not standardized. This means that if you want to integrate multiple MLSs, you will soon find out that the data is submitted differently. For example, the price can be called “ListingPrice,” or “Price” or “Amount.”
  4. Another potential issue is importing the data itself – even if libraries are available, learning how to download and query listing data from RETS can be somewhat tricky.
  5. MLSs tend to have thousands of listings and even more photos – the developer who will assist with the project should have some database design experience before undertaking this type of project.
  6. Lastly, the server you are using should be strong enough to handle tens of thousands of listings, meaning that you’re most likely going to need a Virtual Private Server before going forward.

For this option to work, an agreement is required with the MLS to share data. This agreement will stipulate what you can do with the data and how to use it.

The MLS may also charge you or your client for access to RETS, but that depends on the Multiple Listing Service policy.

Real Estate Standard Organization – RESO API

The Real Estate Standard Organization, or RESO API for short, is a new way to store and transfer listing data from MLS.

The idea behind RESO is to standardize all data exchanged between the different brokerages and multiple listing services and to make sharing such data easier.

The RESO API also features Open Data technology, meaning there’s less need to store vast amounts of data locally.

RESO can also be applied to mobile apps, making it an incredibly powerful tool for developers and agencies who want to build larger, more flexible real estate websites.


As with RETS, before you can use the system, you will be required to contact your local MLS and ask them for credentials.

You may also be required to sign an agreement with the MLS before implementing the system.

However, once the credentials are available, importing properties through RESO is extremely easy and convenient for non-technical realtors and website developers equally.

If you’re exploring real estate technology, you’ll find it useful to understand the distinctions between various systems. I recommend reading ‘How Is IDX Different From RESO Web API?‘ to gain a clear perspective on these key real estate tools.

MLS Import imports properties through RESO API

MLS Import is the import tool. You need to import MLS properties from your MLS to your Real Estate website without using any intermediary plugin or IDX solution.

It’s all you need to use in one package (import properties and get full technical assistance through the entire process, plus automatic synchronization from MLS).

Check out the Real Estate Demos created with MLS Import. Contact us if you are interested to see a demo of MLS Import at work.


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