ads.txt vs sellers.json: two files, two questions they answer

ads.txt vs sellers.json: two files, two questions they answer

Buyers conflate these because both fight spoofing. They verify opposite ends of the chain.

1. ads.txt is published by the publisher. It lists which seller accounts are authorized to sell that domain's inventory. It answers: is this SSP allowed to represent this site at all.

2. sellers.json is published by the SSP/exchange. It maps each seller ID to the actual company behind it, and flags whether they are a PUBLISHER (owns the inventory) or INTERMEDIARY (reselling). It answers: who am I actually buying from, and how many hands has this passed through.

3. SupplyChain object (schain) ties them together in the bid request, listing every node the impression traveled. ads.txt + sellers.json let you validate that chain.

4. When to lean on which — use ads.txt checks to catch domain spoofing (unauthorized sellers claiming a premium domain). Use sellers.json + schain to catch resold inventory and hidden intermediaries inflating your path.

5. A clean ads.txt entry does not mean a short path. The seller can be authorized AND an intermediary. That is the gap most buyers miss.

Why it matters: if you only check ads.txt you stop spoofing but still overpay on long resold paths. If you only read schain you miss the authorization question. Run both against your bid-request logs.