37signals Makes AI Agents the Default Code Writers
Published by AINave Editorial • Reviewed by Ramit
37signals shifts handwritten code to the exception
At the Rails World keynote, Ruby on Rails creator David Heinemeier Hansson said 37signals was “done writing code by hand.” The company’s “pencils down” position makes AI agents the default code writers, while manual coding becomes an exception for cases where an agent cannot produce what engineers want, according to Hansson’s remarks.
He described the change as recognition of what was already happening at the software company, not a new rule that every developer should follow. The distinction matters: 37signals is describing a working norm inside its own company, not declaring handwritten coding obsolete across the industry.
The fallback includes fixing the machine
Hansson’s description of the exception is more revealing than the slogan. When an agent falls short, an engineer can “get the old pencil out” and write the missing code, he said. But the response should then be to “fix the machine,” rather than simply treating manual work as the normal route around the problem, according to the account of his keynote.
That frames agent use as an ongoing engineering process. A human still supplies the code when needed, but the failure also becomes a prompt to address why the agent did not meet the request. The report does not explain which tasks trigger this fallback, or how 37signals evaluates its agents’ output. It also gives no productivity, quality, or cost results, so the policy should not be mistaken for evidence that the workflow has already outperformed manual coding.
A company practice, not a universal verdict
The report names OpenAI Codex, Anthropic Claude Code, and Cursor as examples of tools associated with changes in coding. It does not say that 37signals uses any of those products, or identify the company’s own tool stack. Hansson’s broader point was that figuring out how to reap the rewards of AI was the “serious question” of the moment, as he put it at the keynote.
For engineering teams, the useful idea is the feedback loop, not the phrase “pencils down”: use an agent as the starting point, intervene when it cannot meet the need, and consider what would make the agent succeed next time. That is a stated approach, not a reported measure of its results. The unanswered practical question is how 37signals turns those interventions into changes to its agent workflow.
