Supply-path checks: what ads.txt and sellers.json actually tell you

A buying platform labels an impression “authorized.” The label is useful, but the team still needs to know who is selling the ad space, which intermediaries are involved, and whether the placement meets the campaign’s standards.

Supply-path review examines the route through which advertising inventory reaches the buyer. It helps make the seller relationships understandable before the team draws conclusions about price or quality.

Three pieces of information are often discussed together: ads.txt, sellers.json, and the SupplyChain object. They have different jobs.

Start with the question each file can answer

Information	Main question
ads.txt or app-ads.txt	Which seller accounts has the publisher authorized?
sellers.json	Who is associated with a seller account in an advertising system?
SupplyChain object	Which selling parties are represented in this bid request’s path?

IAB Tech Lab’s ads.txt documentation covers authorization declarations for websites and apps. Its sellers.json documentation explains seller identities and their relationship to the SupplyChain object.

Authorization is one check. It does not establish whether an impression was viewable, reached a real person, appeared in appropriate content, or produced a useful outcome.

Follow a fictional path

Suppose publisher.example lists seller account 1234 for exchange.example. A buyer receives inventory described as coming from that publisher through that exchange.

Start by checking that the domain or app identity is the one the campaign intended to buy. Then match the advertising-system domain and seller account against the publisher’s declaration. Review the corresponding sellers.json record and the selling path supplied with the opportunity.

Do not match only the company’s display name. Similar names and different account IDs can represent different relationships. Keep the identifiers in the investigation record so the exchange or publisher can reproduce the check.

If there is a mismatch, ask for the specific relationship and the evidence needed to resolve it. A missing or inconsistent record deserves investigation; one failed lookup alone does not prove fraud.

Understand DIRECT and RESELLER

In ads.txt, DIRECT describes the publisher’s control of the declared account; RESELLER describes an authorized resale relationship. Do not read DIRECT as “no technology intermediary exists,” or RESELLER as “bad inventory.”

Those labels do not reveal the full fee structure. A longer path may add cost, but path length alone cannot establish the price paid to the publisher or the value delivered by each participant.

Ask the commercial partner for the fee and service information needed for the decision. Treat an unavailable fee as an unknown, not a number to invent from the number of intermediaries.

Compare outcomes on a consistent basis

Imagine two approved paths to similar inventory. Path A has a $4 CPM and Path B has a $5 CPM. The cheaper path is not automatically the better buy if the inventory mix, invalid-traffic treatment, viewability, or outcome measurement differs.

First align the publisher and placement scope, device mix, dates, and measurement definitions. Then compare delivery, quality, cost, and business outcomes. The CPM calculator will check the price calculation; it cannot make unlike inventory comparable.

Avoid changing every path at once. A controlled comparison with an agreed objective is easier to interpret than a sudden account-wide block that also changes the audience and placement mix.

Keep the check current

Publisher relationships and account declarations can change. Record when the evidence was retrieved, which identifiers were examined, and who owns the follow-up.

For a recurring review, prioritize new sellers, unexplained identifier changes, and discrepancies between the declared publisher and the delivered environment. Keep an escalation route to the publisher or selling partner rather than relying on a dashboard label alone.

The programmatic advertising guide explains the broader buyer and seller roles. Use transparency data to establish the route, then use separate evidence to judge the quality of the advertising opportunity.