Jane Street's formal methods, explained

Jane Street, the quantitative trading firm that runs its core systems in OCaml, has written up how formal methods work in their production code. The short version: they're using mathematical proofs and theorem provers to verify that their code does what it claims before it ships. Not unit tests. Not property-based testing. Actual proofs that the logic holds.

The post walks through how they got formal methods into a trading environment where a bug doesn't just crash a service—it costs money. They built tooling to make proof-writing feel less like writing a dissertation and more like writing code. Then they applied it to real systems: routing logic, scheduling, the stuff that keeps their trading infrastructure from imploding at 3 p.m.

The TLDR DevOps angle is that this is infrastructure people can actually learn from. Jane Street isn't doing formal methods for academia's sake. They're doing it because their systems are complex and the cost of getting them wrong is real. If you're already using Terraform for infrastructure as code, the same principle applies: prove your infrastructure before you apply it.

Why this matters for us: Brown and Black engineers who've spent years patching systems into submission are learning that the tools to catch bugs before they hit production exist, and the people building them are treating it as engineering, not theory.