What is an ad network, and how does it show up in seller files?
Part of Supply path transparency
The short answer
An ad network is a company that gathers ad space from many publishers and sells it to advertisers as its own package, setting the price and keeping a margin. When a network sells through an exchange account it controls, publishers list it as RESELLER in ads.txt and the exchange types the account INTERMEDIARY.
Key takeaways
- An ad network buys or represents ad space from many publishers and resells it, which makes it a seller of inventory it does not own.
- An exchange runs an auction between many sellers and many bidders; a network is one more seller that can send its package into that auction.
- When a network sells a site through its own exchange account, the site's ads.txt line says RESELLER and the exchange's sellers.json lists the network as INTERMEDIARY or BOTH.
- Before buying network inventory, ask for the site list, the selling path and whether a direct path to the same sites exists.
What is an ad network?
Definition
- Ad network
- A company that aggregates ad space from many publishers, packages it by audience, topic or format, and sells the package to advertisers under its own terms, paying the publishers a share of what it earns.
The term is older than programmatic buying, and the standards still use it. The OpenRTB 2.6 specification (opens in a new tab) describes its purpose as simplifying the connection between suppliers of publisher inventory, which it lists as exchanges, networks working with publishers and sell side platforms, and competitive buyers, which it lists as bidders, demand side platforms and networks working with advertisers. A network can therefore sit on either side of a trade. In seller files, buyers meet the supply side kind, which represents a set of sites or apps and resells their impressions.
OpenRTB also shows where a network appears in a bid request. Its Publisher object describes the entity who directly supplies inventory to and is paid by the exchange, which may be a publisher, intermediary exchange or ad network. So the seller ID in a request can belong to a network rather than to the site; the site itself is named in the Site or App object.
How is an ad network different from an ad exchange?
The cleanest line is ownership of the sale. An exchange runs an auction where many sellers meet many bidders under published rules; it does not present the inventory as its own product. A network takes the publishers' space into its own catalog, packages and prices it, and is paid as the seller. One company can run both businesses, but in any single transaction a buyer can ask which role each company played.
| Role | What it does | Strength for a buyer | Limit for a buyer |
|---|---|---|---|
| Ad network | Represents or buys space from many publishers and resells it as a package | One contract can reach many small sites a buyer would never sign one by one | The site list, the price paid to publishers and the margin may not be visible |
| Ad exchange | Runs an auction for each impression between connected sellers and bidders | Price is set per impression under stated auction rules | An exchange may know only its direct neighbors, not every company upstream |
| SSP | Works for the publisher: floors, blocks, deals and payment, and can run its own auction | Clear about whose rules shape the bid request | The same company may also run network or reseller accounts |
Publishers still treat networks as a separate kind of demand inside their own ad servers. In Google Ad Manager, Network is one of the line item types, and Google's line item help (opens in a new tab) says to use it for your partner ad networks which don't have an impression goal, serving them by a defined percentage of impressions. From the publisher's side, a network is one more buyer of its remnant space.
How do ad networks appear in ads.txt?
A network can appear in a site's ads.txt file in two ways, and the difference tells a buyer how the money flows. The ads.txt 1.1 specification (opens in a new tab) defines the first field of each line as the canonical domain of the SSP, exchange, header wrapper or other system that bidders connect to, and the second field as the seller or reseller account within that system.
| Line in the site's ads.txt | What it says | What the buyer checks next |
|---|---|---|
| bluebid.example, 88120, RESELLER | Account 88120 on the exchange bluebid.example belongs to someone other than the publisher, here a network, and the publisher allows it to resell the site | The bluebid.example sellers.json entry for 88120 should name the network and type it INTERMEDIARY or BOTH |
| netads.example, site4471, DIRECT | The network runs its own advertising system, and the publisher controls account site4471 inside it | netads.example should publish a sellers.json listing site4471 as PUBLISHER with the site owner's name |
| MANAGERDOMAIN=netads.example, US | The network is the primary or exclusive programmatic seller for the site in the United States | The network's path may be the most direct route to the site in that market |
Some networks operate their own system and bid request pipe, which produces the second pattern. The third line is the ads.txt 1.1 variable for a publisher that hands monetization to one company. IAB Tech Lab's ads.txt 1.1 implementation guide (opens in a new tab) says such managers are generally paid a percentage of the inventory they sell and are expected to appear in the supply chain as the terminal node.
Why does a network show as a reseller?
Because of how the label is defined. RESELLER, in the ads.txt specification, indicates that the publisher has authorized another entity to control the account and resell its ad space through the named system. A network that sells a site through its own exchange seat controls that seat, not the publisher, so the honest line is RESELLER. The same fact appears from the exchange side. The sellers.json specification (opens in a new tab) types an account INTERMEDIARY when the inventory sold through it is not owned by the named entity or the advertising system does not pay them directly, and BOTH when a seller transacts both kinds.
Two rules keep a network path traceable. The sellers.json specification says that when seller_type is INTERMEDIARY or BOTH, the domain field should be the root domain of the seller's own sellers.json file, so the buyer can follow the trail into the network's directory. And the SupplyChain object specification (opens in a new tab) says it is invalid for a reseller to copy the previous seller's chain without inserting its own node. A network that skips either rule leaves a gap the buyer cannot close from the files.
Where do ad networks still matter for apps?
The app standards name networks directly. The app-ads.txt specification (opens in a new tab) groups ad networks and sell side platforms together as bid request issuers, and requires them to include the app's store URL in each request so verifiers can find the developer's website and its file. It also says any ad network that performs authorized seller checks on its own proprietary inventory must use the app store URL in that check.
Inside apps, networks can be called one after another. Google Ad Manager's mediation help (opens in a new tab) describes mediation for mobile apps as a list of yield partners called individually, in sequence, from the app. The same app impression can therefore reach a DSP through several paths, and each path deserves its own check.
What should a buyer ask about network inventory?
Network inventory is not suspect by default; networks give small publishers access to demand they could not sell alone. These questions separate a network that adds reach with a clear record from one that adds a hop and hides the sites.
Questions to put to an ad network before a buy
- The network supplies the full list of sites or apps in the package, not only categories or examples.
- Every listed site authorizes the network's account in its ads.txt or app-ads.txt file.
- The network publishes its own sellers.json, and the sites in the package appear there with named owners.
- Bid requests from the network carry a SupplyChain object that includes the network's own node.
- The network says whether any site in the package also sells directly on an exchange the buyer already uses.
- The network says how sites are added or removed during a flight and how the buyer is told.
- Confidential entries are explained, and a named path is offered where one exists.
What does a network review look like on a real plan?
Fictional example
An independent jeweler in central Pennsylvania
A fictional family jeweler with stores in Lancaster, Harrisburg and Allentown wants display ads beside wedding planning, local events and lifestyle content read in central and eastern Pennsylvania, in English. A regional ad network offers a package of local wedding and lifestyle sites, and the agency asks for the site list before pricing.
The planner opens each listed site's ads.txt file. Most carry a RESELLER line for the network's seat on a large exchange, and that exchange's sellers.json types the seat INTERMEDIARY with the network's domain. The network's own sellers.json lists each site with its owner, so those paths are clear.
Two sites in the package have no line for the network at all, so the planner drops them and asks the network why they were offered. A third site sells directly on the exchange the trading desk already uses, so the agency buys it on that direct path and keeps the network for the small sites it could not reach alone.
Can PlacementGraph show when a network resells a site?
Frequently asked questions
Is an ad network the same as a DSP?
No. A demand side platform is software a buyer uses to bid on impressions across many exchanges. OpenRTB lists networks working with advertisers among the buyers of inventory, but a supply side network sells space it gathered from publishers, while a DSP buys for an advertiser.
Does an ad network have to publish a sellers.json file?
When it acts as an advertising system, yes by the standard. The sellers.json specification says every advertising system listed in an ads.txt file, and any system referenced from a SupplyChain node, should publish one at its root domain. A network that only holds seats on other exchanges appears in their files instead.
Can a network sell a site that does not list it in ads.txt?
It can try, but buyers that enforce ads.txt will not bid. Google's Display & Video 360 help, checked in October 2026, says the platform checks every seller in the SupplyChain object, intermediaries included, against the publisher's file and blocks inventory resold by unauthorized sellers.
Why would a network mark a seller as confidential?
The sellers.json specification lets an advertising system hide a seller's name and domain with is_confidential set to 1, while still requiring every seller to be listed. Networks that represent individual site owners sometimes use it. The buyer sees the seller ID but cannot confirm who is paid.
Sources
- OpenRTB 2.6 specification (opens in a new tab)IAB Tech Lab
- ads.txt Specification Version 1.1 (opens in a new tab)IAB Tech Lab
- ads.txt 1.1 Implementation Guide (August 2022) (opens in a new tab)IAB Tech Lab
- sellers.json specification (opens in a new tab)IAB Tech Lab
- OpenRTB SupplyChain object (opens in a new tab)IAB Tech Lab
- Authorized Sellers for Apps (app-ads.txt) (opens in a new tab)IAB Tech Lab
- Line item types and priorities (opens in a new tab)Google Ad Manager Help
- Introduction to Open Bidding (opens in a new tab)Google Ad Manager Help
- Authorized Digital Sellers (opens in a new tab)Google Display & Video 360 Help
Researched and written by PlacementGraph Research. Read how we research, source and update these pages. Corrections: diana@placementgraph.com.