It’s tax season for Americans, and apparently it’s audit season for digital media.

Alphabet Inc.’s Google is committing to a series of audits for its web video powerhouse YouTube by the ad industry’s measurements watchdog, the Media Rating Council. Less than two weeks ago, Facebook also announced it had agreed to have some of its ad metrics audited by the MRC.

Specifically, Google said the MRC will audit the way that three independent metrics companies—Moat, Integral Ad Science and DoubleVerify—collect data measuring whether video ads are viewable on YouTube and how long they are viewed. Those audits will evaluate everything from the technology being used and how it’s integrated on YouTube’s website and app to the way the data is crunched.

In addition, Google plans to have the MRC audit data for ads on non-Google sites purchased via two key Google ad buying tech platforms—AdWords and DoubleClick Bid Manager.

These audits should be welcome news in the digital ad industry, where marketers have been pushing for more transparency and overall assurance that the ads they pay for end up where they are supposed to and can be seen by consumers.

Companies like Google and Facebook, which dominate the online ad industry, have faced criticisms that they have been “grading their own homework” because they have traditionally collected and self-reported so much of their own viewer data. While marketers lean on third-party metrics companies that have approval to work with the platforms, those metrics firms aren't always allowed to directly do their own measurements and instead receive and record data provided to them by YouTube or Facebook.

“Our data has to be trusted and comprehensive. We are very in tune with the idea,” said Babak Pahlavan, Google’s senior director of product management, analytics solutions and measurement. Mr. Pahlavan said that Google’s move had been in the works for years and wasn't a reaction to industry pressure or Facebook’s recent announcement.

Given YouTube’s scale (it reaches a billion people and every day its users stream hundreds of millions of hours of videos), it’s a massive challenge to conduct such integrations, but the goal is to complete the process over the next two quarters, Mr. Pahlavan added.

He noted that Google has already had 30 of its various ad metrics audited by the MRC—including for several other YouTube ad products—and has been working with the measurement standard-bearer for more than a decade. “We’ve been investing in trust for a long time,” he said.

Over the past several years, a large number of media companies have agreed to work with third parties like Moat or DoubleVerify to track viewability data. And these third parties have individually been audited by the MRC.

But because giant platforms like YouTube and Facebook have been reluctant to implement third party tracking code from these vendors directly, there has been some ongoing frustration in the ad buying community that these companies’ data is less transparent than others.

On top of that, Facebook has had a number of embarrassing data tracking mishaps, adding to the noise surrounding third party measurement and fueling the idea that the web’s biggest ad platforms play by their own rules.

“What’s happening now is that this data is generally in the control of large platforms, and it’s a little bit of a black box,” said DoubleVerify President and Chief Executive Wayne Gattinella, who added that his company has been working on helping Google provide more transparent metrics for roughly a year.

“The market is saying, ‘We want to ensure that the process [these companies employ] is understood, and is documented and accurate. Otherwise, it could be garbage in garbage out, and we’re not able to determine that.’ So this is all good news.”

Bob Liodice, chief executive of the Association of National Advertisers, a trade group for marketers, agreed and called Facebook’s and Google’s recent audit commitments “a turning point.”

Mr. Liodice said that last year’s bombshell report on the overall lack of transparent practices in the ad agency world, along with a recent speech by Procter & Gamble’s Chief Brand Officer Marc Pritchard calling for the industry to clean up its act, have combined to elevate the data transparency issue.

“The digital media supply chain is in bad shape, and people are taking good hard looks, asking, ‘Is this the best way to spend my money?’” he said.

Mr. Liodice said he hopes Google’s and Facebook’s moves help put more advertisers’ minds at ease and potentially demystify the way they operate.

“Why would you want to be called a walled garden?” he said. “That’s a horrible reputation to have. You want to be seen as open. If you look like you have something to hide, that’s not a good place to be.”

Write to Mike Shields at mike.shields@wsj.com

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