September 2023 · By Andrew Sutherland
I was recently asked what makes a great engineer, and I liked what I wrote so I decided to post it! Here is my list.
A great engineer has worked on the same system for multiple years. They've seen systems evolve. They’ve learned what choices or shortcuts they made were worthwhile, and which have caused problems. They’ve seen their choices confuse other engineers. They’ve had to fix performance issues on code they wrote six months ago. You can’t get great without this iteration.
One basic interview test is how fast and capable an engineer is with their editor. Do they know their keyboard shortcuts? Do they know their terminal well? A good engineer will not stand for a slow editing environment, slow save-refresh loops, slow tests, slow deploy processes, or slow code review processes. If you can’t work quickly, it’s very hard to do good work. A great engineer will stop what they’re doing (within reason) and fix problems with their tools before moving forward.
They themselves are in the room when user testing. They reply to support tickets and get on video calls with users. They care! At Quizlet, many great engineers were previous Quizlet users and so had good default intuition. Even then, nothing beat visiting a classroom. They would see kids or teachers totally misunderstand a new interface they were building. They would see a slow-loading page cause a kid to start distracting another kid. They might see a bug in a bugtracker, but when they watch a kid hit it and get frustrated in front of them, a great engineer will often fix that same-day. A user-centered engineer takes time to develop their intuition so they can see well beyond what can be written explicitly in a product spec.
Engineers should be proactive in bringing new ideas to the team. They might spend a weekend prototyping a new interface concept they thought of. They might come to their team and say, we can’t keep building on this page, it need to be rearchitected, and here’s how we should do it. When building a new login screen, they proactively cover every edge case not previously discussed or specced. They do the right thing without slowing down to ask for permission.
A great engineer will say when the product they’re building isn’t good enough yet. Annoyingly for management, often when a product is 95% done is when the real interesting work starts. When you’ve checked all the important boxes, but the product just doesn’t feel great yet, you want engineers to push for better. I saw this mistake happen sometimes at Quizlet: we’d ship when something was good enough. It wouldn’t get a ton of traction. We'd iterate a bit more, but not make major changes. Then people would say, well, that didn’t work. In consumer products, users need to be delighted or they’ll move on.
A great engineer makes other engineers great too. That means they’ll pair program or mentor other engineers both ad-hoc and formally. They’re great at code reviews - they push on conceptual problems with code, not just cosmetic problems. They’ll push on people to write better tests and to rewrite their code if it’s confusing. They’ll research new patterns or tools and educate their team on how to use them. They’ll write and maintain documentation.
Many problems have an easy solution and a hard solution. A great engineer will sometimes say we can live with a quick/expedient solution to a problem. But often they need to go spelunking: traversing different layers of code to find a root cause. They are unafraid to explore areas they’ve never touched before, and they won’t rest until they’ve found the root cause of an issue. What appears to be an occasional and simple UI glitch might go much deeper. It could be a problem caused by only-in-production hot cache keys concentrated on one server. You need engineers willing to traverse from the front-end layer (maybe the UI is making repeated requests and that’s the real problem) to the app layer (maybe the cache key distribution algorithm is wrong) to the server layer (maybe the network is configured to rate-limit more than expected).