RentCast API vs Spark API for AI agents
RentCast API is a self-serve REST API for US property records, value and rent estimates, market data, and active sale and rental listings. FBS's Spark API and RESO Web API give authorized applications access to MLS data on the Flexmls/Spark platform.
The short answer
- RentCast API: The quickest self-serve way to search active US rentals and for-sale homes with agent contacts, without MLS paperwork.
- Spark API: Apps built for agents, brokers or MLSs that use Flexmls, where the MLS member authorizes access.
Side by side
| RentCast API | Spark API | |
|---|---|---|
| Searches | Active sale and rental listings by city or area with filters, plus 150+ million property records, valuations and market trends. | MLS listings (and, for VOW apps, sold data) from participating MLSs, within the roles each MLS grants. |
| Returns | Listing records with address, coordinates, property type, beds, baths, size, price or rent, status, days on market, MLS name and number, history, and listing agent and office. | MLS listing records in Spark or RESO Web API format. |
| Before the first call | A RentCast account and an API key from the dashboard; no MLS membership or license. | A free developer account, then an MLS data plan or an MLS member who authorizes your app. |
| Free | Developer plan: 50 API calls a month for $0. | Developer account sign-up is free. |
| Paid | Foundation plan: $74 a month for 1,000 requests. | $50 a month for each MLS you access, once you have data from your first MLS (MLS data plans may set their own terms). |
| Acting on a result | Listings include the listing agent's and listing office's name, phone, email and website; no landlord contact is described. | Not stated on its pages |
| Limits on keeping or showing results | The API terms allow storing API data in your own systems and redistributing it only as the license section permits; no attribution is required. | No storing MLS content except temporary caching for performance, unless your key permits replication; MLS display rules and license terms apply. |
| Coverage | US nationwide; listings are gathered from public sources, not directly from MLSs. | Participating MLSs on the FBS platform; no list or count on its pages. |
| MCP server | Official hosted MCP server: https://developers.rentcast.io/mcp | No official server listed |
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 RentCast API?
A RentCast account and an API key from the dashboard; no MLS membership or license.
Is RentCast API free?
Developer plan: 50 API calls a month for $0.
What do I need before I can use Spark API?
A free developer account, then an MLS data plan or an MLS member who authorizes your app.
Is Spark API free?
Developer account sign-up is free.
Sources
Every line about another company comes from its own pages. Prices and terms change, so check the source before you rely on one.
RentCast API, read on October 15, 2026:
- rentcast.io/api: “Our pricing plans start with 50 free API calls per month”
- rentcast.io/api: “$ 74 Per Month”
- rentcast.io/api: “Active sale and rental listings across the country.”
- developers.rentcast.io/reference/introduction: “To get started, create a RentCast account to access your API dashboard and generate your first API key.”
- developers.rentcast.io/reference/introduction: “We have nationwide coverage for most residential properties and select commercial property types in the US”
- developers.rentcast.io/reference/property-listings: “the names and contact information of the listing agent, the listing office or broker”
- developers.rentcast.io/reference/property-listings: “we do not retrieve our property listing data directly from the MLS”
- rentcast.io/terms-api: “and (v) to incorporate and store the API Data within your internal systems”
- rentcast.io/terms-api: “neither use of the RentCast API nor use of the API Data requires attribution”
- developers.rentcast.io/reference/ai-tools: “The RentCast API MCP server is hosted at https://developers.rentcast.io/mcp.”
Spark API, read on October 15, 2026:
- sparkplatform.com/docs/overview/api: “The Spark API allows authorized MLS members to request data through developer applications”
- sparkplatform.com/docs/overview/api: “When IDX applications are purchased, the MLS member must authorize that application to access their data.”
- sparkplatform.com/docs/overview/faq: “It’s free to sign up for a Spark API developer account.”
- sparkplatform.com/docs/overview/faq: “Once you have access to data from your first MLS, API access costs $50/mo for each MLS you can access.”
- sparkplatform.com/docs/terms_of_use/developer_agreement_and_terms_of_use: “except for temporary caching purposes necessary for performance enhancement”
- sparkplatform.com/docs/terms_of_use/developer_agreement_and_terms_of_use: “Compliance with MLS Rules and License Terms regarding MLS Content”