Faced with a rising backlash over the spread of disinformation in the aftermath of the 2016 elections, Facebook last year came up with a seemingly straightforward solution: It created an online library of all the advertisements on the social network.

Transparency, it decided, was the best disinfectant.

Ads would stay in the library for seven years, letting ordinary users see who was pushing what messages and how much they were paying to do it. Facebook gave researchers and journalists deeper access, allowing them to extract information directly from the library so they could create their own databases and tools to analyze the ads — and ferret out disinformation that had slipped past the social network’s safeguards.

“We know we can’t protect elections alone,” Facebook said when it unveiled the latest version of its Ad Library in March. “We’re committed to creating a new standard of transparency and authenticity for advertising.”

But instead of setting a new standard, Facebook appears to have fallen short. While ordinary users can look up individual ads without a problem, access to the library’s data is so plagued by bugs and technical constraints that it is effectively useless as a way to comprehensively track political advertising, according to independent researchers and two previously unreported studies on the archive’s reliability, one by the French government and the other by researchers at Mozilla, the maker of the Firefox web browser.