European publishers show 73% adoption of supply chain transparency standards

IAB Europe released comprehensive research findings on August 7, 2025, revealing that 72.64% of European web publishers have implemented ads.txt files, marking significant progress in digital advertising supply chain transparency. The study, which examined 2,054 European online news publishers, demonstrates widespread adoption of industry standards designed to combat ad fraud and enhance transparency in programmatic advertising.

The research evaluated three critical supply chain transparency standards developed by IAB Tech Lab: Authorized Digital Sellers (ads.txt) files, sellers.json files, and the SupplyChain object. These standards enable verification of commercial relationships between publishers and ad tech intermediaries while preventing monetization of counterfeit inventory.

According to the study's findings, "At least 72.64% of European web publishers in the sample hosted ads.txt files." These files allow publishers to declare which ad tech companies can legitimately monetize their inventory, creating a verification system that helps buyers reject fraudulent impressions before placing bids.

Technical implementation reaches high accuracy rates

IAB Europe's analysis revealed exceptional technical compliance among participating publishers. After automated and manual verification processes, researchers found that "99.83% of lines were found to be valid" in the collected ads.txt files. This high accuracy rate indicates that publishers have successfully implemented the technical specifications despite the complexity of the standards.

The validation process involved parsing 1,492 ads.txt files using automated systems that flagged errors in format, missing components, or invalid relationships. Common error categories included missing commas, incorrect attribute ordering, and invalid relationship definitions that failed to specify either "DIRECT" or "RESELLER" relationships.

Cross-reference validation shows strong correlation

The study's most significant finding emerged from cross-referencing ads.txt declarations with corresponding sellers.json files. Researchers successfully matched approximately 79% of valid ads.txt lines with sellers.json entries, confirming commercial relationships between publishers and advertising technology intermediaries.

This correlation rate demonstrates that supply chain transparency standards are functioning effectively across the European digital advertising ecosystem. The sellers.json standard, published by exchanges and supply-side platforms, provides the mirror image of publisher declarations by revealing every seller they represent.

Technical challenges affect data collection

Despite overall success rates, the research identified several technical obstacles that affected data collection. Sellers.json collection succeeded in approximately 61% of attempts, with failures largely attributed to errors in ads.txt files containing incorrect ad system domains.

The study documented various error types affecting ad system domains, including spelling mistakes, incorrect top-level domains, and formatting issues that prevented proper file loading. These technical challenges highlight areas where publishers can improve implementation accuracy.

Industry context and broader adoption trends

The European findings align with broader industry efforts to enhance supply chain transparency. IAB Tech Lab previously announced upgrades to its Supply Chain API, introducing near real-time data delivery through increased crawl frequency from three to five days per week.

Additionally, the organization has expanded CTV app store support by adding Samsung, Vizio, and LG to its App-Ads.txt aggregator, demonstrating continued growth in transparency initiatives across different advertising channels.

The research builds on previous industry studies, including comprehensive analyses by TAG and ANA that revealed persistent transparency challenges throughout the programmatic media supply chain.

Demand-side standards face implementation hurdles

While supply-side transparency standards show strong adoption, demand-side equivalents face different challenges. The buyers.json file and DemandChain object standards, formally launched in 2024 after development beginning in 2021, require careful coordination across supply chains before achieving effectiveness.

These standards transmit technical signals from advertisers to help publishers identify legitimate buyers and reduce fraudulent advertising risks. However, their implementation requires synchronized adoption across multiple intermediaries to create functional transparency pathways.

Recommendations emerge for ecosystem improvement

The study identified specific recommendations for publishers and ad systems to improve transparency implementation. Key suggestions include ensuring ads.txt and sellers.json files remain accessible in root domains, excluding them from robots.txt restrictions, and implementing validation procedures for format correctness.

For publishers, the research emphasizes validating that ad system domains host legitimate sellers.json files and ensuring proper comment formatting using '#' symbols. Supply-side platforms received recommendations to maintain loadable sellers.json files and provide accurate domain information.

Certification schemes support transparency goals

The broader supply chain transparency effort incorporates multiple industry initiatives beyond technical standards. Certification schemes such as IAB Ireland Gold Standard, IAB Sweden Gold Standard, and Digital Ad Trust in France provide additional verification layers for participating companies.

These certification programs ensure that adtech intermediaries and publishers effectively implement technical standards and best practices, including the Transparency & Consent Framework and IAB Tech Lab's supply chain transparency requirements.

TCF enforcement shows measurable impact

IAB Europe's Transparency & Consent Framework (TCF) compliance programs demonstrate concrete enforcement results. In 2024, over 400 enforcement procedures targeted participating organizations for non-compliance, resulting in temporary suspension of more than 20 entities until they remedied identified issues.

Suspended organizations face tangible consequences, including inability to seek user consent, directly impacting their operational capacity and revenue generation. This enforcement approach helps elevate overall compliance levels while isolating actors that fail to meet established standards.

Privacy regulations drive transparency adoption

The accelerating adoption of supply chain transparency standards coincides with increasing privacy regulations across European markets. Publishers and advertisers increasingly recognize transparency tools as essential for compliance with data protection requirements and maintaining consumer trust.

Recent developments in programmatic advertising growth show 72% of marketers planning to increase programmatic investment in 2025, making supply chain transparency increasingly critical for maintaining advertiser confidence and regulatory compliance.

Future outlook for transparency initiatives

Industry experts anticipate continued growth in transparency standard adoption as regulatory pressure increases and advertisers demand greater supply chain visibility. The success of supply-side implementations provides a foundation for accelerating demand-side standard adoption through coordinated industry efforts.

The research methodology employed web scraping tools while respecting established guidelines, including robots.txt compliance and rate limiting. This approach ensured comprehensive data collection while maintaining ethical research practices across the 2,054 publisher sample.

Timeline

• December 2023: ANA releases comprehensive programmatic media supply chain transparency study highlighting industry challenges
• April 2024: IAB Tech Lab enhances Supply Chain API with increased crawl frequency and near real-time data
• May 2024: Amazon Publisher Services unveils new transparency tools including Transparent Ad Marketplace expansion
• July 2025: Industry leaders emphasize transparency during IAB Europe Virtual Programmatic Day, noting shift toward deal-based purchasing
• August 7, 2025: IAB Europe publishes comprehensive Q&A on digital advertising supply chain and European publisher transparency study

PPC Land explains

Supply Chain Transparency: The practice of providing visibility into the various intermediaries and relationships within the digital advertising ecosystem. This concept enables advertisers and publishers to understand the complete path their ads take from buyer to end-user, including all fees and intermediaries involved. Supply chain transparency helps combat fraud by allowing parties to verify legitimate commercial relationships and reject counterfeit inventory before transactions occur.

Ads.txt (Authorized Digital Sellers): A technical standard that allows publishers to publicly declare which companies are authorized to sell their digital advertising inventory. Publishers host these files on their websites, listing every exchange or reseller permitted to monetize their impressions. This standard enables buyers to verify legitimate sellers and reject counterfeit inventory before placing bids, serving as a foundational tool for supply chain verification.

Sellers.json: A complementary transparency standard published by exchanges and supply-side platforms that reveals information about every seller they represent. This file serves as the mirror image of ads.txt, providing certification details under industry schemes and enabling cross-reference validation. When matched with ads.txt declarations, sellers.json files confirm commercial relationships between publishers and advertising technology intermediaries.

Publishers: Content creators and website owners who monetize their digital properties by making advertising inventory available for sale. Publishers range from major news organizations to independent bloggers, all seeking to generate revenue from their content through programmatic advertising. They play a crucial role in supply chain transparency by implementing standards like ads.txt and selecting trustworthy advertising technology partners.

IAB Tech Lab: The global digital advertising technical standards organization that develops the frameworks enabling supply chain transparency. This entity creates and maintains standards including ads.txt, sellers.json, and the SupplyChain object, working with industry stakeholders to establish common protocols. IAB Tech Lab's standards facilitate verification of commercial relationships and help prevent fraudulent activities across the advertising ecosystem.

Programmatic Advertising: The automated buying and selling of digital advertising inventory through technology platforms and algorithms. This method enables real-time bidding on ad placements, allowing advertisers to target specific audiences across millions of websites and applications. Programmatic advertising's complexity necessitates transparency standards to ensure legitimate transactions and prevent fraud within the automated ecosystem.

Ad Fraud: Illegitimate activities designed to generate false advertising revenue through counterfeit inventory, fake impressions, or misrepresented commercial relationships. Supply chain transparency standards specifically target ad fraud prevention by enabling verification of legitimate sellers and publishers. Common fraud types include domain spoofing, where bad actors impersonate legitimate publishers to steal advertising revenue.

Supply-Side Platforms (SSPs): Technology platforms that help publishers manage, optimize, and sell their digital advertising inventory to multiple buyers simultaneously. SSPs connect to various demand sources and exchanges, conducting real-time auctions to maximize publisher revenue. These platforms implement transparency standards by maintaining sellers.json files and facilitating verification of their publisher relationships.

Commercial Relationships: The business agreements and partnerships between different entities in the digital advertising supply chain, including publishers, advertisers, and technology intermediaries. Transparency standards enable verification of these relationships to ensure that advertising transactions involve legitimate parties. Clear documentation of commercial relationships helps prevent unauthorized reselling of advertising inventory and maintains trust throughout the ecosystem.

European Digital Advertising Market: The regional advertising ecosystem spanning European Union countries and the broader European Economic Area, subject to specific privacy regulations and transparency requirements. This market faces unique challenges including GDPR compliance, diverse language requirements, and varying national regulations. The European market serves as a testing ground for transparency initiatives that often influence global advertising standards and practices.

Summary

Who: IAB Europe researchers evaluated 2,054 European online news publishers to assess supply chain transparency standard adoption

What: Study found 72.64% of publishers implemented ads.txt files with 99.83% technical accuracy and 79% successful matching with sellers.json data

When: Research findings published August 7, 2025, following data collection and analysis of European publisher websites

Where: European digital advertising market, focusing on online news publishers across multiple countries and markets

Why: Growing need for supply chain transparency to combat ad fraud, ensure legitimate commercial relationships, and meet regulatory requirements in programmatic advertising