SPO Auditor

An open-source supply-path transparency auditor. It checks who actually sold each impression, against ads.txt, sellers.json, and the OpenRTB SupplyChain Object (schain), and flags unauthorized sellers, hidden hops, and fee-leaking resold paths.

The gap this fills

Supply-path transparency is a 2026 flashpoint: buyers cannot see what curators and exchanges actually do, or what fees they take. The primitives to check it already exist, ads.txt (who a publisher authorizes to sell its inventory), sellers.json (who an exchange's seller IDs really are), and the schain object (the disclosed chain of intermediaries). What is missing is an open tool that ties them together. This is that tool.

How it works

Feed it a bid log (impressions, each carrying a supply chain), the publisher's ads.txt, and the exchange's sellers.json. For every impression it walks the chain and checks each hop:

• Is the seller authorized in the publisher's ads.txt? (If not, someone is selling inventory they should not.)
• Is the seller ID actually in sellers.json, and is it disclosed or confidential?
• Is the chain complete, or are there hidden hops?
• How many reseller hops sit between the buyer and the publisher (where fees leak)?

Then it scores each path 0..1 and summarizes the findings.

Quickstart (bundled sample data)

pip install -e .
spo-auditor audit --sample

The sample set includes a clean direct path, an unauthorized seller, a resold multi-hop path, an incomplete chain, and a seller missing from sellers.json, so you see every finding type at once.

Audit your own data:

spo-auditor audit bidlog.json --ads-txt publisher_ads.txt --sellers-json exchange_sellers.json

What it flags

Code	Meaning	Severity
unauthorized_seller	Seller not declared in the publisher's ads.txt	high
not_in_sellers_json	Seller ID absent from the exchange's sellers.json	high
incomplete_chain	schain.complete is 0, hops are hidden	high
excessive_hops	More intermediaries than the configured limit	medium
confidential_seller	Seller is marked confidential in sellers.json	medium
reseller_hop	Authorized but resold, not a direct path	low

Relationship to adcp-trader

AdCP products do not carry supply signals (reach, hops, authorization). This auditor produces exactly those signals, so it is the natural enrichment source for the adcp-trader supply-path rule.

License

MIT. See LICENSE.