Supply path optimization from the buyer’s side

The same ad impression can reach your DSP through several different routes, each with its own intermediaries, fees and risks. If you never look at those routes, you are paying for duplication you cannot see. This guide walks through how supply paths form, which signals reveal them, and a set of practical steps buyers can take to clean them up.

Why the same impression arrives more than once

A supply path is the chain of companies between the publisher and your demand-side platform (DSP, the software you use to buy programmatically). In the simplest case, a publisher works with one supply-side platform (SSP), which sends a bid request straight to your DSP. In practice, the publisher may work with several SSPs, and some of those SSPs may also receive the same inventory from resellers, ad networks or other exchanges.

Each company in the chain is a “hop.” Every hop can add a fee, add latency and add another place where data is lost or altered. When a publisher’s inventory is available through several paths at once, your DSP may see multiple bid requests for what is really one impression. You end up bidding against yourself, and your auction data gets noisier.

Supply path optimization (SPO) is the practice of choosing which routes you want to buy through and cutting the rest. The goal is not the fewest possible sellers. The goal is the most direct, most transparent and most reliable route to the inventory you actually value.

The signals that make paths visible

IAB Tech Lab created three standards that, together, let a buyer reconstruct a supply path. You do not need to be an engineer to use them, but you do need to know what each one tells you.

• ads.txt and app-ads.txt: files published by websites and apps that list which companies are authorized to sell their inventory, and whether each relationship is DIRECT (the publisher’s own account) or RESELLER (someone selling on the publisher’s behalf).
• sellers.json: a file published by SSPs and exchanges that lists the sellers they work with, whether each is a publisher, an intermediary or both, and (ideally) the seller’s name and domain.
• SupplyChain object (schain): a field inside the bid request that records every company that handled the request on the way to you, one “node” per hop.

The value comes from cross-checking. The schain tells you who claims to have touched the request. The sellers.json files tell you who those companies are. The publisher’s ads.txt or app-ads.txt tells you whether the publisher actually authorized them.

Reading a supply chain in practice

When you pull log-level or path-level data from your DSP, look at each schain and ask a short series of questions.

1. Is the chain complete? The schain object carries a flag indicating whether all nodes are present. An incomplete chain means at least one company did not pass its information along.
2. How many nodes are there? A single node usually means the SSP bought directly from the publisher. More nodes mean resellers are involved. More is not automatically bad, but each extra node needs a reason to exist.
3. Does every seller ID resolve? Look up each seller ID in the corresponding sellers.json. If an ID is missing, or marked confidential with no name or domain, you cannot verify who you are paying.
4. Does the publisher authorize it? Match the SSP domain and seller account ID against the publisher’s ads.txt or app-ads.txt. A path the publisher never authorized is a path you should not fund.
5. Is the relationship type consistent? If ads.txt says RESELLER but sellers.json lists the account as a PUBLISHER, something is misconfigured or misrepresented.

Doing this manually for a handful of top domains is a good exercise. At scale, you will want your DSP or a verification tool to run these checks automatically and surface exceptions.

Practical SPO steps for buyers

Once you can see paths, you can shape them. These steps work whether you run an in-house trading desk or work through an agency.

Start with your spend, not the whole open web

Pull the domains and apps that carry most of your spend. SPO effort pays off fastest where you already buy heavily, and it keeps the analysis manageable.

Pick preferred paths per publisher

For each important publisher, identify the paths that are authorized, complete and short. Where a publisher sells DIRECT through several SSPs, you do not necessarily need all of them. Choose based on transparency, fee disclosure and the quality of data you receive.

Apply allowlists at the path level

Many DSPs let you target or block specific SSPs, seller IDs or schain patterns. Use those controls to prefer direct paths and exclude unverified resellers. Revisit the list on a schedule, because publisher partnerships change.

Use curated deals where they fit

Private marketplace deals and curated packages can collapse many paths into one known route. They also make it easier to hold a seller accountable, because the terms are explicit. The trade-off is less reach, so reserve them for inventory where quality matters most.

Ask sellers direct questions

Ask SSPs and marketplaces how they source supply, whether they resell other exchanges, how they populate schain, and what fees apply along the path. A partner who answers clearly is easier to trust than one who points you to a dashboard.

Mistakes that undo the work

SPO can go wrong in predictable ways. Watch for these:

• Cutting too hard. Blocking every reseller can remove legitimate paths, such as a publisher’s chosen partner for a specific format. Check authorization before you cut.
• Treating short as clean. A one-hop path from an unauthorized seller is still a bad path. Authorization and transparency matter more than node count.
• Ignoring in-app and CTV. App-ads.txt and schain apply beyond the browser, but adoption and data quality can vary. Apply the same checks, and expect more exceptions.
• Setting and forgetting. Sellers.json files and ads.txt files change constantly. A path that was authorized last quarter may not be today.
• Optimizing only for price. The cheapest route may carry weaker brand safety or fraud checks. Measure outcomes, not just CPM.

A clean supply path is easier to build when the marketplace you buy from is built around transparency. Vortex Media runs a curated marketplace across web, in-app and CTV with transparent supply paths and published ads.txt, app-ads.txt and sellers.json files, so buyers can verify the route before they spend. See how that works on our advertisers page.