Ian on Software Engineering at Jane Street

I’m Ian, a developer in Jane Street’s London office, and I started full-time in 2019. I work as a desk developer: I sit on a trading desk and build tools specific to that desk, often using tools built by core development teams.

I think of Jane Street as roughly one-third traders, one-third developers and one-third other functions, including legal, accounting and recruiting. Traders are organized into desks by asset class, such as stocks or bonds, while developer teams build particular sets of tools or applications.

Writing code is a big part of the job, but so is reading it. Jane Street has a code-review culture: at least one other person reads every change in full, and usually several others read parts of it. I probably spend at least as much time reading code and giving feedback as I do writing it.

Another part of the job is specifying features and projects: talking to users, gathering requirements and thinking about design. We consider what the team will build next week, next month and next year, so that current projects contribute to a bigger picture and address things users cannot yet do.

There is also support work. Once tools are deployed, things sometimes go wrong and we have to find bugs and roll out fixes. Those incidents can be stressful, though I find them exciting; the amount of support work varies substantially by team.

Intern projects are released to production and remain in use. I use some code written by interns I have mentored every day. Even a project that does not succeed can still provide value by showing us that an approach is not tractable.

Programming and software engineering courses that teach software design and coding are the most useful preparation. Distributed systems or database courses can help too, but I think core software engineering matters most; other things are relatively easy to learn on the job.

New developers go through an OCaml boot camp. Exercises begin with basics such as defining functions and variables and progress to systems that consume Jane Street market data or serve multiple RPCs synchronously. Afterward, people move on to real projects.

Code review continues the learning process after boot camp. Colleagues review your code and suggest more idiomatic OCaml or libraries you may not have known about. That feedback is a major source of ongoing development.

My users are mostly traders who sit a few feet away. It is easy to show them prototypes, get feedback and iterate. When a tool is released they often use it the same day and quickly ask for the next feature or point out what is still missing.

I enjoy how engaged those users are. A change may reach fewer users than at a larger software company, but those users care a lot about it, readily give feedback and come over to discuss what we should build next.

Jane Street also organizes social events. In London we have a regular pub evening called the Bull and Camel, and teams organize dinners for visitors, new joiners or simply to catch up. When visiting an office such as New York or Hong Kong, colleagues are often happy to socialize and show you around the city.