Supply Path Optimization: How DSPs Use sellers.json

Every impression your SSP sells travels through a supply path. Publisher to SSP to DSP. Sometimes publisher to SSP to reseller to another SSP to DSP. The path matters because every hop adds cost, latency, and opacity.

DSPs figured this out years ago. The result is supply path optimization, the process of mapping every available path to a given impression, scoring each one, and routing spend to the best options. SPO went from a conference buzzword to a standard DSP capability. And the data that powers it? A significant portion comes from sellers.json.

For SSPs, SPO isn't something that happens to other people. It's the process that determines whether your platform gets a DSP's budget or whether the DSP routes around you entirely.

What SPO Actually Does

SPO is a DSP-side process for reducing the number of supply paths they buy through. The motivation is straightforward: when a DSP can reach the same publisher inventory through five different SSPs, buying through all five means:

• Duplicate auction costs: Bidding on the same impression five times wastes infrastructure and budget
• Higher effective CPMs: Multiple intermediaries each take a cut
• Increased fraud exposure: More paths mean more opportunities for bad actors
• Harder verification: Five paths mean five sets of ads.txt and sellers.json entries to cross-check

SPO solves this by ranking paths and concentrating spend on the top performers. A DSP might evaluate 30 SSPs that can reach a publisher and decide to route 80% of spend through the top 3.

The SSPs ranked 4 through 30 don't get an email explaining why spend dropped. The DSP just stops bidding, or bids less aggressively, through those paths. The SSP sees declining win rates and revenue without understanding the root cause.

How DSPs Build the Supply Path Map

Before a DSP can optimize, it needs to map every path to every publisher. This is where sellers.json becomes critical.

Step 1: Crawl ads.txt Files

The DSP fetches ads.txt from every publisher domain where it wants to buy inventory. Each ads.txt line declares an SSP and account ID with a DIRECT or RESELLER relationship.

Step 2: Crawl sellers.json Files

For every SSP mentioned in those ads.txt files, the DSP fetches the SSP's sellers.json. Each entry reveals the seller's identity, domain, and relationship type.

Step 3: Build the Graph

The DSP combines ads.txt + sellers.json + SupplyChain (schain) object data to construct a graph of every path from publisher to DSP. Each node in the graph is an entity (publisher, SSP, reseller). Each edge is a verified relationship.

Step 4: Score Each Path

The DSP scores paths based on multiple factors: number of hops, verification completeness, historical performance, cost efficiency, and transparency.

Step 5: Route Spend

The DSP concentrates spend on the highest-scoring paths and reduces or eliminates spend through low-scoring ones.

sellers.json data feeds directly into Steps 2, 3, and 4. If your sellers.json is incomplete, stale, or heavily confidential, the DSP's map of your supply paths has gaps. Gaps lower your score. Lower scores mean less spend.

The Factors DSPs Evaluate in sellers.json

Not all sellers.json files are created equal. Here's what DSPs actually look at when scoring your supply paths.

Transparency Ratio

What percentage of your sellers are non-confidential? DSPs can fully verify non-confidential entries (name, domain, seller_type). Confidential entries are black boxes.

DSPs increasingly treat high confidentiality as a negative signal. If 40% of your sellers are confidential, the DSP can't verify 40% of the bid requests coming through your platform. That's a trust problem.

The industry average sits around 20-25% confidential. Top-performing SSPs in SPO evaluations typically run below 10%.

Verification Alignment

When a publisher lists your-ssp.com, 12345, DIRECT in their ads.txt, does your sellers.json show seller_id "12345" with seller_type PUBLISHER and the publisher's domain? Or is there a mismatch?

BeamFlow's analysis shows that 24% of ads.txt entries fail sellers.json cross-verification. From a DSP perspective, each mismatch is a supply path it can't fully trust. DSPs running SPO penalize SSPs with high mismatch rates.

Path Length

DSPs prefer shorter paths. A DIRECT relationship (publisher holds the account on your SSP) is one hop. A RESELLER chain (publisher to reseller to your SSP) is two or more hops.

Your sellers.json reveals path length through seller_type. A file dominated by INTERMEDIARY entries tells the DSP that most of your supply comes through resellers, meaning longer paths with more intermediaries taking margins. DSPs prioritize SSPs where a higher percentage of sellers are PUBLISHER (direct relationships).

File Freshness

DSPs cache your sellers.json and re-crawl periodically. If your file hasn't changed in months while publishers have been adding and removing entries, the DSP's cached data drifts from reality. Stale data means stale verification, which means lower confidence.

DSPs notice when files update frequently versus rarely. An SSP that updates sellers.json daily signals active management. One that updates quarterly signals neglect.

Seller Coverage

How many of the seller_ids in bid requests actually appear in your sellers.json? If a DSP receives bid requests from your platform with seller_ids that don't exist in your file, those requests fail verification immediately.

Incomplete seller coverage usually means onboarding is faster than sellers.json updates. A publisher signs up, starts sending traffic, but their seller_id doesn't appear in your file for days or weeks.

How DSPs Make the Cut

DSPs approach SPO with different levels of aggressiveness, but the pattern is consistent: evaluate, rank, consolidate.

Evaluation

DSPs build scorecards for each SSP. The scorecard combines sellers.json data quality with performance metrics (win rate, viewability, fraud rate, cost efficiency). sellers.json data feeds the trust and transparency dimensions of the scorecard.

Ranking

SSPs get ranked within each publisher or each vertical. The DSP doesn't need a global ranking. It needs to know, for Publisher X, which SSP provides the most trustworthy and efficient path.

Consolidation

The DSP concentrates spend on the top-ranked SSPs and reduces bids or stops bidding through the rest. Some DSPs hard-cut SSPs below a threshold. Others gradually shift budget over time.

The result: SSPs that score well in SPO see steady or growing share of DSP spend. SSPs that score poorly see declining revenue without an obvious cause.

What SSPs Can Do About SPO

SPO is a DSP-side process. You can't directly influence it. But you can control the inputs that DSPs use to evaluate you.

Make your sellers.json excellent

This is the most direct lever. Reduce confidentiality, fix domain mismatches, align seller_types with publisher ads.txt declarations, and update frequently. Every improvement in your sellers.json data feeds directly into DSP SPO evaluations.

Prioritize direct publisher relationships

DSPs prefer PUBLISHER entries over INTERMEDIARY entries because they represent shorter, more transparent paths. Growing your direct publisher base improves your seller_type ratio and your SPO score.

Eliminate stale entries

Remove sellers who are no longer active. Every stale entry is potential verification noise that hurts your overall data quality signal.

Communicate transparency to DSP partners

Some DSPs will share SPO criteria if asked. Reach out to your DSP partners and ask what they evaluate. Use that feedback to prioritize your sellers.json improvements.

Monitor your competitive position

You can't improve what you don't measure. Track your sellers.json data quality over time and compare it against industry benchmarks. BeamFlow's SSP audit tool provides this comparison across 2,000+ sellers.json files.

The Trend: Fewer SSPs, Higher Standards

The programmatic industry is consolidating supply paths. Major DSPs have publicly stated they're reducing the number of SSPs they buy through. The Trade Desk, DV360, and Amazon DSP have all made moves to concentrate spend on fewer, better-verified supply paths.

This trend accelerates. As DSPs cut SSPs, the remaining SSPs capture more volume. The cut SSPs lose revenue and market share. The gap widens.

For SSPs, the takeaway is direct: sellers.json data quality is no longer a compliance exercise. It's a competitive survival factor. The SSPs that treat sellers.json as strategic infrastructure, investing in accuracy, transparency, and freshness, are the ones that survive SPO consolidation.

The ones that treat it as a checkbox file that gets updated when someone remembers? They're the ones getting cut.

Frequently Asked Questions

Do all DSPs run SPO?

Most major DSPs do, but with varying sophistication. Some use automated algorithms that evaluate hundreds of data points. Others use simpler rules-based approaches. The trend is toward more automation and more frequent re-evaluation.

Can a small SSP compete against large SSPs in SPO?

Yes. SPO evaluations are often per-publisher, not global. A small SSP with strong direct relationships and a clean sellers.json can score higher than a large SSP for specific publishers where the small SSP has better data quality.

How quickly does SPO respond to sellers.json improvements?

It depends on the DSP's re-evaluation cycle. Some DSPs re-run SPO analyses weekly. Others do it monthly or quarterly. Improvements in your sellers.json won't have an overnight effect, but they compound over weeks and months.

Will DSPs tell me my SPO score?

Some will, if you ask. DSPs with dedicated SSP partnership teams often share scorecard data. Others treat it as proprietary. Either way, the factors they evaluate are well-known, and improving your sellers.json data quality improves your score regardless of whether you see the number.

Is there a relationship between sellers.json quality and fraud rates?

Indirectly, yes. SSPs with poor sellers.json data quality tend to have higher fraud rates because verification gaps create opportunities for bad actors. DSPs know this correlation and factor it into SPO evaluations.