UNDER ALL IS THE DATA | PART 3 OF 8
Two Licenses, One Compilation
Stop thinking of IDX and VOW as website types. Start reading them as the license grants they are.
By Saul Klein and John Reilly August 2026
Parts 1 and 2 gave you the history and the concept. This part gives you the vocabulary the rest of the series runs on. The fastest way to understand the difference between IDX and VOW is to stop thinking of them as website types and start thinking of them as two different licenses carved out of the same copyrighted asset: the MLS compilation. The MLS typically owns the compilation, database, photographs, remarks, statistics, and all, and it leases participants the right to use it. IDX and VOW are the two defined uses under which compilation data leaves the system and reaches consumers over the Internet. Everything that distinguishes them flows from what each license permits, who grants it, and who is the consumer on the other end.
IDX: The Advertising License
The legal essence of IDX is broker to broker. Each listing broker licenses every other participant to display their active, pending, and publicly accessible sold listings on websites, apps, and audio devices the displaying broker controls. The permitted use is narrow: display so consumers can identify properties they may be interested in purchasing, personal and non-commercial, full stop. The consumer is anonymous, with no relationship and no obligations. Because it is advertising, the grant is presumed but revocable. Consent is deemed given unless a listing broker affirmatively opts out, and reciprocity enforces the bargain: withdraw your listings from the pool and you lose the right to display everyone else’s. Every IDX site is, in legal substance, a licensed advertisement of the compilation.
VOW: The Brokerage Services License
VOW is a brokerage services license, and it is compulsory. That was the decree’s whole point. The MLS must deliver the feed on cost based, non-discriminatory terms, and no participant may opt their listings out of it. Only the seller can withhold, and only Internet wide. The permitted use is fundamentally different: not advertising to the anonymous public, but delivering actual brokerage services to a consumer with whom the broker has first established a lawful broker-consumer relationship. That is why the license reaches deeper into the compilation. The VOW consumer may see substantially what a client sitting across the desk would see, including Sold listings, subject only to the enumerated confidential fields.
And the VOW license carries a mandatory downstream sublicense: the Terms of Use, under which every registrant accepts personal non-commercial use, no copying or retransmission, a bona fide purchase or sale interest, and express acknowledgment of the MLS’s copyright in the database. The IDX visitor is an audience. The VOW registrant is the last licensed link in the data chain.
Side by Side
| IDX | VOW | |
| License type | Advertising and display license | Brokerage services delivery license |
| Grant | Broker to broker reciprocal pool, administered by the MLS; consent presumed, revocable by the listing broker | MLS to participant, compelled by mandatory NAR policy; no broker opt out; seller only withholding |
| Consumer | Anonymous public; no registration, no obligations | Registered, credentialed end user bound by Terms of Use |
| Data scope | Active, pending, and publicly accessible sold listings; display fields only | Full client deliverable dataset, less enumerated confidential fields, including sold data |
| Use limit | Identify properties of interest; personal, non-commercial | Deliver brokerage services within an established relationship |
| Currency | Refresh at least every 12 hours | Refresh at least every 3 days |
| Enforcement | Reciprocity: opt out and you cannot display others’ listings | Registrant records, audit trails, credential production on MLS demand |
The one line version: IDX licenses the compilation to attract a customer. VOW licenses the compilation to serve one.
Read the acronyms as licenses and every rule you have ever grumbled about, refresh cycles, attribution, disclaimers, registration, record retention, stops being trivia and becomes the predictable consequence of the grant. It also sharpens the question we have been circling since Part 2. If IDX consent is the listing broker’s to give and revoke, and the VOW feed is compulsory, then on the question of Internet display, who actually holds the pen? Part 4 walks the answer, which is a menu, and every item on it belongs to one party.
Next in the series: Who Holds the Pen, on the seller’s menu of display choices.
