MLS vs IDX

The MLS is the database; IDX is a permission to display part of it. Your board’s Multiple Listing Service is the cooperative system of record where members enter and manage listings, and IDX, short for Internet Data Exchange, is the licensing framework that republishes a defined slice of that system, active listings only, on member websites. You never put “the MLS” on your site. You put a licensed feed on it, and the board decides what that feed contains.

One is a system, the other is a licence

The cleanest way to hold the distinction: the MLS exists whether or not you have a website, and IDX exists only because websites do. The MLS is where a listing is born — entered by the listing brokerage, visible to every member of the board, carrying far more information than the public ever sees. IDX came later, as the answer to a specific question: under what terms may members advertise each other’s active listings on their own public sites? The answer is a reciprocity deal plus a data agreement, and that agreement — not the MLS itself — is what your website actually connects to.

What the IDX slice deliberately leaves out

An IDX feed is a subset by design, and knowing the exclusions saves confused support tickets later. Off-market records — solds, leases, expired and terminated listings — sit in a separate VOW lane that requires visitor registration before any of it renders. Listings whose sellers declined internet display are absent from every member site. And boards typically reserve part of the field set even on active listings, licensing a fuller record to the registered-visitor lane than to the public one. So the gap between what you see as a member and what your site shows a visitor is policy, not a defect. The IDX website explainer walks the public slice in detail.

Where realtor.ca fits between the two

Realtor.ca is neither the MLS nor IDX — it is CREA’s national advertising portal, fed by listings that members share to it. The portal shows a consumer-facing subset of many boards’ inventories, while your IDX feed shows one board’s active inventory in full, minus opt-outs. That is why neither surface is a superset of the other: a listing can appear on your site but not the portal, or the reverse, without anything being broken. There is also a national syndication feed (CREA’s DDF) that redistributes portal-level listings to member sites, and it gets confused with IDX constantly — but it carries opt-in listings at portal depth, not a board’s full active inventory. For a website serving one market, the practical consequence is the same in both cases: a direct board feed beats syndication on depth and freshness where your business actually lives.

Why the distinction matters when you buy a website

Because vendors blur it, and the blur hides the questions that matter. “MLS integration” on a sales page can mean a direct board feed, a third-party aggregator, or a thin national-syndication layer, and the three behave very differently on freshness, completeness, and compliance. Once you know that the MLS is the source and IDX is a specific licensed lane, the vendor conversation sharpens into checkable questions: which board’s feed, which lane, who holds the agreement, and how fast changes propagate. The Canadian playbook for getting listings onto your own domain — boards, agreements, and the role your brokerage plays — is laid out in MLS listings on your website.

The one-sentence version

The MLS is the market’s shared memory; IDX is the narrow, rule-bound window your website is allowed to open onto it — and everything about running a good listings site follows from respecting which side of that window each piece of data lives on.