SimplyRETS vs ATTOM Property API for AI agents
SimplyRETS is a developer API and WordPress plugin that turns your own MLS's RETS or RESO Web API feed into a simple REST listings API. ATTOM Property API is a REST API for US property records: ownership, sales history, valuations (AVM and rental AVM), mortgages, schools, crime and neighborhood data.
The short answer
- SimplyRETS: An affordable, simple REST layer for an agent or brokerage that already has its own MLS data feed.
- ATTOM Property API: Deep public-record and valuation data on any US property, rather than finding homes currently on the market.
Side by side
| SimplyRETS | ATTOM Property API | |
|---|---|---|
| Searches | Listings from the MLS feeds you connect: active, under contract, pending and closed; residential, condo, rental, multifamily, commercial and land, plus open houses. | Properties by address, parcel number, ATTOM ID or latitude/longitude; the docs describe last sales, sales history and valuations, not active for-sale or rental listings. |
| Returns | Listing records with property details, photos, and listing agent and office information when the MLS feed supplies it. | JSON or XML property records with characteristics, ownership, sale history, AVM values and area data. |
| Before the first call | RETS or RESO Web API credentials from your MLS; whether you must be an agent or broker depends on the MLS. | A trial sign-up to receive an API key; production plans through ATTOM. |
| Free | Free demo API keys with sample data; no free trial with live data. | 30-day free trial with an API key. |
| Paid | Basic plan $49 a month, plus a one-time $99 fee per MLS connection. | Not stated on its pages |
| Acting on a result | Listing agent and office contact details come with each listing when the MLS feed has them, and some MLSs require showing them. | Nothing: no agent, landlord or listing contact fields are described. |
| Limits on keeping or showing results | Only listings flagged for IDX display are served, and you must follow the display rules (e.g. last-updated disclaimers) set by your MLS. | Use of data is governed by a separate license agreement that is not published on the site. |
| Coverage | Whatever MLS you connect (US); no fixed national coverage. | US, 160+ million properties. |
| MCP server | No official server listed | ATTOM MCP Server (access arranged through ATTOM): https://www.attomdata.com/solutions/delivery/mcp-server/ |
Where Openpath fits
Openpath has no homes listed yet. Owners and landlords can list a home for rent or sale on Openpath today, free, and agents will find it through the same search as jobs and businesses. Get listed.
Questions people ask
What do I need before I can use SimplyRETS?
RETS or RESO Web API credentials from your MLS; whether you must be an agent or broker depends on the MLS.
Is SimplyRETS free?
Free demo API keys with sample data; no free trial with live data.
What do I need before I can use ATTOM Property API?
A trial sign-up to receive an API key; production plans through ATTOM.
Is ATTOM Property API free?
30-day free trial with an API key.
Sources
Every line about another company comes from its own pages. Prices and terms change, so check the source before you rely on one.
SimplyRETS, read on October 15, 2026:
- simplyrets.com: “These are our demo API keys, you can use them!”
- simplyrets.com: “Each RETS or RESO Web API connection requires one time $99 connection fee.”
- simplyrets.com: “Get RETS or RESO Web API credentials from your MLS”
- simplyrets.com/faq: “This is dependent on the MLS area you want to connect to.”
- docs.simplyrets.com/topics/fields-and-features-for-idx-compliance: “In some cases it may be required that you show the contact information for the listing agent and/or listing office.”
- docs.simplyrets.com/topics/fields-and-features-for-idx-compliance: “in many areas it’s required to show the timestamp of when the data was last updated in a disclaimer.”
- simplyrets.com: “Basic $ 49 /mo”
- simplyrets.com/faq: “We don't currently offer a free trial period with live data”
ATTOM Property API, read on October 15, 2026:
- attomdata.com/solutions/property-data-api: “Sign up for a free 30-day trial to receive an API key and explore ATTOM’s extensive property data”
- attomdata.com/solutions/property-data-api: “Covering 160+ million U.S. properties and 99% of the U.S. population”
- attomdata.com/solutions/property-data-api: “ownership information, lat/long, square footage, loan types, sales history, sales comps, crime, schools and more”
- api.developer.attomdata.com/docs: “return information pertaining to the most recent sale of a property or list of properties”
- attomdata.com/solutions/property-data-api: “The ATTOM MCP Server provides AI-native access to ATTOM Intelligence through the Model Context Protocol (MCP).”
- attomdata.com/solutions/delivery/mcp-server/how-it-works: “Access is governed, permissioned, and centrally managed”
- attomdata.com/terms-of-use: “subject to the terms of a separate license agreement”