Are there any viewability measurement tools that validate ads.txt and app-ads.txt in real time?

Yes — some ad verification / viewability measurement platforms can also check ads.txt and app-ads.txt in real time, but it’s not universal. In practice, these checks are often bundled into broader inventory quality, fraud detection, or supply-path verification tools rather than pure viewability products.

Examples of vendors/features that commonly include this kind of validation:

• DoubleVerify
• Integral Ad Science (IAS)
• MOAT / Oracle Moat
• Pixalate
• Protected Media
• CH-Verify / other supply-chain verification vendors

A few important caveats:

• “Real time” can mean different things: some tools check at bid/request time, while others crawl or sync frequently and surface near-real-time alerts.
• ads.txt/app-ads.txt validation is usually about whether the seller of the impression is authorized, not about viewability itself.
• In-app verification may be less direct than web verification because app-ads.txt is hosted on the developer’s domain and must be matched to the app store listing.

If you want, I can give you:

1. a vendor-by-vendor comparison, or
2. a shortlist specifically for web vs in-app.