The aim is to understand the political "dark ad" - an electioneering message, derived from internet data, that targets specific groups, right down to the micro-level.
"It's clearly an issue that resonates with a lot of people," Knight-Webb told AFP at his work space near the British parliament.
"There's a lot of people trying to understand how they're being manipulated."
After Prime Minister Theresa May in April announced a snap general election, Knight-Webb designed the programme and founded a group called 'Who Targets Me?' with Sam Jeffers, a business consultant.
More than 6,500 people have downloaded his extension, covering 630 constituencies - almost all of the 650 up for grabs in the vote on June 8.
"This is the largest study of its kind ever carried out to my knowledge," said Knight-Webb, who plans to extend the project to elections in Germany in September as well as to Brazil, the Czech Republic and Italy.
He hopes the project will encourage people "to be sceptical about the advertising they're receiving, to get outside of their bubble a bit more and understand what the rest of the country is seeing".
Micro-targeting of digital ads to particular groups has come under scrutiny after being used by the victorious Brexit campaign last year and by Donald Trump's team in its campaign for the US presidency.
Spending returns published by Britain's independent Electoral Commission showed that the Vote Leave campaign spent 40 percent of its £6.8-million budget ($8.8 million, 7.8 million euros) on the services of Canadian digital marketer AggregateIQ.
Leave.EU, which also campaigned for Brexit, denied it had hired a similar group, Cambridge Analytica, which then worked on the Trump campaign, saying its contacts with the company had been informal.
Gerry Gunster, who worked on the Leave.EU campaign, has hailed Facebook's role as a "game changer".
"You can say to Facebook, I would like to make sure that I can micro-target that fisherman in certain parts of the UK so that they are specifically hearing that if you vote to leave that you will be able to change the way that the regulations are set for the fishing industry," Gunster told BBC Panorama.
"Now I can do the exact same thing for people who live in the Midlands who are struggling because the factory has shut down. So I may send a specific message through Facebook to them that nobody else sees," he said.