Curl is the perfect example of open source software that is undervalued.
It’s almost certain that you’ve used curl (Client URL) today, probably without knowing it. Every time your phone connects to 5G, your printer prints something, or your car receives a firmware update, curl plays a role. Even when satellites receive information from Earth, there’s a process involved somewhere in the background. You can see it as the silent engine of our digital world.
If you’ve never heard of the software, the name Daniel Stenberg probably means nothing to you either. The man has been maintaining his project since 1996 but receives hardly any recognition for it. The software is in almost every device we use daily.
Early Beginnings
Stenberg vertelt in zijn keynote op het Open Source Summit 2025 hoe zijn verhaal ooit begon: “Met ongeveer 100 regels code, ergens in 1996, ging ik van start.” Hij was van plan om een simpele manier te bedenken waarmee bestanden op het internet gezet konden worden. Dertig jaar later telt dat script 180.000 regels, geschreven door 1.400 bijdragers. Curl mag dan wel open source zijn, want “het is ontworpen voor maximale verspreiding”, Stenberg is de enige persoon die er voltijds mee bezig is.
Companies sometimes forget that we are volunteers.
Daniel Stenberg, curl
Curl is therefore a library that transfers and receives data over internet protocols such as http, FTP, and dozens of others. It allows our devices and applications, from apps to operating systems, to talk or communicate with each other. This is because it has an MIT license: the software can be freely used, modified, and registered, including in commercial products.
Present Everywhere, Even on Mars
It’s hard to grasp how ubiquitous curl actually is, especially if, like me, you’ve never heard of it. It’s literally everywhere. In printers, GPS systems, tablets, medical devices, routers, game consoles, cars, and phones… It’s too much to list. Even NASA’s Mars rover robot uses it to send data. Stenberg says it’s almost impossible to find a device with an internet connection without curl.
Op zijn blog verduidelijkt Stenberg dat er volgens hem gemiddeld 16,5 curl-installaties zijn in ieder huishouden. Zijn berekening stelt dat dat er in totaal 50 miljard installaties zijn wereldwijd, waardoor de curl-servers maandelijks 65 miljard verzoeken moeten verwerken.
Man without a Name
Stenberg doesn’t have a company, a large budget, or marketing. He works from his attic in Sweden. That’s a disadvantage of open source: some software is almost crucial to our digital life, but the contributors often remain unknown. Companies like Google, Apple, Tesla, BMW, Sony and dozens of others including 47 car brands use curl in their products, but don’t really acknowledge the work.
“Many open source projects remain underfunded and more than overloaded. Maintenance takes time, the responsibility is heavy, and support is virtually nonexistent,” says Stenberg. Another example is the Log4j controversy from a few years ago. When a vulnerability arises, he receives hundreds of emails from manufacturers asking for a solution. “There’s nothing legally wrong with that, but they forget that we are volunteers.”
The big names sometimes even refer people directly to Stenberg when they have questions, while Stenberg doesn’t want to be a helpdesk at all. He treats every question seriously: “I always try to make it educational and explain how the open source community actually works and how they can collaborate with it instead of just using it.”
Keep Smiling
His goal in speaking at conferences is actually to create awareness about how dependent we have become on software maintained by volunteers. One person can make millions of devices work or stop working, yet the optimism that Stenberg radiates is contagious. “Open source gets stronger year after year,” he says. “We build on each other’s work, and we can be proud of that.”
Maintenance takes time, the responsibility is heavy, and support is virtually nonexistent.
Daniel Stenberg, curl
He refers to messages he receives from people who do know what he does and means, and reads one with a smile: “I wrote an application with your libcurl library. I want to thank you for that easy, fast, and good library. I am eleven years old and don’t have much experience, but you make it possible.”
That attitude is admirable, as the man has been working full-time for almost thirty years. To still be proud of what you do after all those years, with minimal recognition and no support, is not given to many people. Tech companies earn billions from their products that work partly thanks to curl. Stenberg and hundreds of others remain sitting alone at their desk at home, surviving on dedication.