Mastering ORTB2 Blocking in Prebid Server: Practical Guide for Publishers

Ad quality and brand safety are persistent challenges for publishers managing programmatic inventory. Despite using Prebid Server or Prebid.js, you may encounter unwanted ads—whether from competitive domains, sensitive categories, or disruptive creatives—that slip onto your site due to inconsistent enforcement across bidders.

The ORTB2 Blocking module offers publishers granular tools to prevent these issues before they impact user experience or breach direct deal agreements. This post breaks down how publishers and ad ops teams can leverage this module to take control over the ad ecosystem, with hands-on configuration tips and real-world examples.

Understanding ORTB2 Blocking: What It Does and Why It Matters

The ORTB2 Blocking module empowers Prebid Server users to block or filter bids at multiple levels, ensuring tighter control over which advertisers, creatives, or apps appear on your site or in your apps. Unlike relying solely on supply-side partners or Google’s Ad Manager blocking, this module offers a publisher-side safety net, enforcing your preferences consistently regardless of bidder implementation.

Blockable Entities Explained

ORTB2 Blocking covers five core attributes based on OpenRTB 2.5:

– Advertiser domains (badv): Block specific advertiser websites.
– Advertiser categories (bcat): Block entire IAB ad categories like “Gambling” or “Alcohol.”
– App bundles (bapp): Prevent mobile app ads from specified bundles.
– Creative types (btype): Block specific ad formats (e.g., rich media, pop-unders).
– Creative attributes (battr): Block attributes like autoplay audio or expandable banners.

Each attribute can be set globally, at account-level, or even for specific bidders, giving fine-grained control.

How ORTB2 Blocking Works in Practice: Execution and Configurations

ORTB2 Blocking operates at two key points in the auction flow: when outgoing requests are sent to bidders (injecting blocking settings), and when incoming bid responses are evaluated (enforcing those blocks). This layered approach allows for both proactive filtering and reactive enforcement—all managed by publisher-controlled config files, not by vendors.

Common Configuration Scenarios

– Block certain competitors across all ad slots but allow them on specific PMP deals.
– Require all bids to declare their advertiser domain; drop any bid that omits it to ensure traceability.
– Enforce stricter blocking for certain bidders known for non-compliance.
– Tailor blocking rules to specific formats (e.g., stricter on video units).

For example, you might block “bad.com” globally, but permit it only through a specific deal or for a certain media type—essential for maintaining programmatic guaranteed or PMP relationships.

Sample Config Implementation

In a PBS-Java setup, an account config could look like this:
– “blocked-adomain”: [“competitor.com”, “fraudad.com”],
– “enforce-blocks”: true,
– “allowed-adomain-for-deals”: [“trustedpartner.com”],
– “action-overrides”: allow more restrictive blocks just for certain bidders like “bidderA” or “bidderB.”

PBS-Go config follows the same logic but with underscore-style keys. Publishing teams can update these configs themselves without code changes or vendor tickets.

Practical Limitations and Advanced Use Cases

While ORTB2 Blocking is powerful, it has a few technical boundaries and nuances every publisher team should know before deploying at scale.

Edge Cases & Enforcement Gaps

Some attributes, like creative types (btype), can only be blocked on outgoing requests—not enforced on bid responses—because this data isn’t always passed back in a usable way. Others, like unknown advertiser domain or category, require explicit enforcement settings to reject non-transparent bidders.

Overrides can apply based on bidder, media type, or specific deal IDs. This reduces the risk of over-blocking high-value deals or key partners but does require careful config hygiene.

Integration with Analytics and Troubleshooting

ORTB2 Blocking generates analytics tags when enforcement events occur. These are valuable for ad ops teams to track which bidders or bids were blocked, why, and under what rules—supporting troubleshooting, compliance audits, or vendor conversations.

Real-World Implementation: Examples and Pitfalls

Translating technical rules into real-world results is where ad ops teams face most surprises. Here’s how ORTB2 Blocking is typically applied—and where things can go wrong.

Header Bidding Flow Example

A publisher enables ORTB2 Blocking to filter out all gambling ad categories (e.g., IAB-7). Bidders receive blocking instructions, but one bidder responds without declaring the ad category. If “block-unknown-adv-cat” is set to true, Prebid Server will drop this bid—protecting the publisher even when a bidder isn’t fully transparent.

Common Publisher Mistakes

– Not updating configs as new competitors or categories emerge, leading to outdated blocks
– Overly broad blocks that unintentionally suppress high-performing campaigns
– Assuming blocking is enforced by all bidders—some only honor request-level blocking, so response enforcement is crucial
– Failing to use deal overrides, which can break key PMP deals if not implemented

Tip: Regularly review analytics data and refresh your config to balance revenue and brand safety.

What this means for publishers

Implementing ORTB2 Blocking empowers publishers to take proactive control over their monetization stack, reducing reliance on third-party enforcement or inconsistent SSP behavior. It directly increases brand safety, brand suitability, and compliance with direct deal obligations. By configuring these rules at the publisher or account level, you avoid unwanted surprises in your ad slots, limit exposure to regulatory risks, and maintain trust with both advertisers and users.

Practical takeaway

If you manage header bidding, make ORTB2 Blocking a core part of your Prebid Server config. Start by mapping out your business-critical blocks—domains, categories, or formats—then implement granular rules and use deal overrides judiciously. Ensure enforcement is enabled where needed, not just configuration, so you catch non-compliant bids at response time.

Routinely monitor enforcement analytics to spot gaps or unintended impacts, and coordinate with ad ops to tune blocking for optimal revenue without sacrificing brand safety. Keep configs reviewed and updated alongside your business needs—ORTB2 Blocking is only as effective as your operational discipline.