Résumé

Tried to protect Duolingo from various spam and abuse threats as the sole full-time employee on the case (others would join during an outage/"war room".)

I was kinda all over the place here technologically. Got some (more) experience in Android and browser frontends as I added a CAPTCHA to protect the sign-up flow (with a tiny dip of the toes in iOS.) It was my first time using a paid DDoS product as well. Shout out to Fastly for being really nice to work with. And of course did my standard backend type work in Python (and some Java.)

Did some standard anti-spam & abuse protections work for user-generated content by finding existing signals, analyzing them to discover decent combinations and thresholds that seemed to differentiate known good accounts vs known bad accounts, and then used those thresholds to create rules to deny probable spammers from doing a protected action ("posting", creating an account, etc.)

Well the English Test product got real popular over the pandemic so the first bit of this was just scaling the tech and making sure it didn't fall over. There wasn't as much to do here as I initially feared besides watch the numbers go up as we built it well, and there are only so many students taking English exams even if you hit 100% market share. Still 20x growth over a month or two can make any SWE nervous. Excited, but nervous.

Shortly thereafter the main goal became ensuring the integrity of our test in terms of anti-cheat functionality. I founded and headed up that team. We moved the app from being browser-based to an ElectronJS desktop app. This let us keep a lot of our familiar webdev-y code of which the company had an excellent pool of talent, and I could focus on providing a good C++ glue layer to give us access to desktop APIs in TypeScript land for all the anti-cheat signals we needed.

An interesting engineering challenge to be sure, but probably my favorite part was mentoring all the new hires that came on at that time and growing them with good tasks suitable to their level. By the time I left the team was more than capable to operate without me.

Oh yeah, I also lead the company internal Python users group during this time as well as helped maintain the internal Python library used by Duolingo's backend services.

A simpler time - or perhaps one with different challenges. The English Test team was still a singular team and not a sub-org at Duolingo. Market share was quite small and all we were trying to do was get noticed by the big universities and attract more users.

Worked on ads and setting up our ads/performance marketing team for success - mostly by setting up metrics tracking and doing 1001 UI and product experiments. Did get us 80% YoY growth, though this would be dwarfed soon enough. Also did a good bit of JavaScript/TypeScript bloat reduction that improved our load performance (30%). Got some "free" SEO and ads cost reduction (-35%) from that. Always nice to see real world goodies come from performance improvements. It appeases my engineering soul I think.

Also got my first taste of mentorship when the first junior engineer joined the team. Soon they were the ones doing the 1001 UI experiments though I did help them transition the code base to TypeScript and React.