“Anyone can edit Wikipedia ,” the adage goes. But, it turns out, a relatively small number actually do.

What is worthy of a digital page in the world’s largest and most-read encyclopedia is decided by roughly 270,000 active volunteers, enthusiasts who populate the online resource with information on anything from 19th-century medicine to TikTok trends. Inevitably, some subjects are sidelined – the global south, notable women – but a new batch of Wikipedian recruits are waging war on one neglected topic: the arms industry.

Last week, in a classroom in central London, two dozen volunteers huddled around laptops and free servings of vegan Ethiopian food for what is known as a “wikithon”, an event of collective and in-person Wikipedia editing. Some were veteran editors in their 70s, others young students who had never registered an account before.…