The journalistic dilemma of how to fact-check national candidates on the debate stage has cropped up again and again in the 2024 election.

Should CNN’s moderators — who were relatively passive when President Biden debated former President Donald J. Trump in June — have been quicker to interject? Should ABC’s moderators — who politely but firmly clarified several of Mr. Trump’s outlandish claims at the second debate on Sept. 10 — have stayed quiet?

Moderation is an art, not a science. But CBS News, host of Tuesday’s vice-presidential matchup between Senator JD Vance and Gov. Tim Walz, is using technology to try something new.

A QR code — the checkerboard-like, black-and-white box that can be scanned by a smartphone — will appear onscreen for long stretches of the CBS telecast. Viewers who scan the code will be directed to the CBS News website, where a squad of about 20 CBS journalists will post fact-checks of the candidates’ remarks in real time.

The code will appear only on CBS; viewers who tune in on a different channel will not see it. (Nearly every major network will simulcast the debate, starting at 9 p.m. Eastern.) But it is a novel approach to guide viewers, already accustomed to watching TV while hovering over a smartphone or laptop, to supplemental journalistic material elsewhere.

“The idea is to give people that second-screen experience,” said Claudia Milne, the senior vice president for standards and practices at CBS News, adding, “The audience can get the takeaway they need in a responsible and smart way.”