URL transparency is the process by which URL of page vehicules are made available for agencies and advertisers. URL transparency can be an issue with ad exchanges, ad network and RTB where it is not the website but the audience which is bought by advertisers. URL transparency allow marketers to know where ads are displayed - at website and webpage levels.
For ensuring URL transparency, a publisher has to make sure his SSP or yield management system is making the URL available while transmitting ad calls to networks or ad exchanges.
Some publishers don’t want to ensure URL transparency to advertisers for preventing channel conflicts - see blind buy. In this case brand safety may still be partially ensured by some tools and services through context analysing or anonymous verification of URLs.