<b>Measuring supply path quality with entropy</b>

<b>Measuring supply path quality with entropy</b>

Supply path optimization (SPO) is choosing the fewest, cleanest routes from your DSP to a given publisher instead of buying the same impression through five resellers. Most teams audit SPO by counting paths. A sharper tool is borrowed from information theory: entropy.

1. For one publisher domain, list every seller path you won impressions through and the share of spend each carries.
2. Compute the spend distribution's concentration. One dominant path equals low entropy; spend evenly smeared across many resellers equals high entropy.
3. High entropy for a single domain is a red flag — it means you are buying the same audience through many intermediaries, each taking a cut and each a place where a bid request could be misrepresented.

Why entropy beats a raw path count: a publisher legitimately sold through two SSPs (an exchange that represents publisher inventory) is fine. The same publisher appearing across nine paths with spend spread thin is reseller sprawl, even though both are 'multiple paths.'

The action is to collapse toward the lowest-entropy route that still gives you scale — usually the direct or near-direct seller with the highest declared sellers.json relationship.

<b>Why it matters:</b> entropy turns a vague 'we should consolidate paths' into a ranked list of domains where consolidation recovers the most margin and removes the most spoofing surface.