Nikolay Feldman

Fullstack software engineer

ReactJs/NextJs+Redux, Android/Kotlin/Java, iOS/Swift

NodeJs, Scala+Play

Additional experience:
Unit/Integration/UI testing, Reverse engineering, Shell scripting, Unix server management, Python, Protobuff, C/C++, C#, PHP, SQL

Yahoo Mail

Implemented various amounts of new features and design changes for the 20+ million daily active users of the Yahoo Mail android app. Primary focus on notifications which have the biggest impact on DAUs, engagement, and ultimately revenue.

Close collaboration with various product/engineering managers, designers, and engineers across multiple teams. Gave Dev Talks and Demos to Org members and leadership on new features and interests such as reverse engineering APKs. On rotation for build watching, release management and monitoring. Mentored junior teammates and interns. Actively interview potential candidates. Always reviewing code to ensure highest quality of code is merged. Submitted a patent request.

Find app on the Play Store

Kung Fu Chess

Online real-time fast paced variant of chess without player turns for Android. Play multiplayer with friends/randoms, or singleplayer against a built-in AI chess engine of varying difficulties.

Rated 4.5 with 70 reviews on the Play Store. 7k+ total unique users since launch, 700+ monthly active users with 10 minute average engagement time. 2 million chess moves made and 1.3 million chess pieces captured by users in over 81k+ matches.

Built with the LibGDX game framework and Kotlin as the client language, with NodeJs handling the server-side game state, matchmaking state, and logging.

Find app on the Play Store

Popchat bot on Kik


Launched PopChat for Yahoo - a fun chatbot designed to provide personal assistance through the Kik chat platform. Ranked 2nd overall on Kik's bot shop, handling over 25 Million messages, peaking at ~500 requests per minute. Proxied 200k+ messages between users. Discontinued Nov 30, 2017.

Bot application server built using Scala, Play framework, and Akka clustering with focus on scalable functional programming.

Ran a separate backend in python to use dlib+tensorflow to perform on-the-fly transformations on images given by users. Trained a facial recognition model containing 13 points around the forehead, totaling 81 facial landmarks which enabled more accurate transformations around the head. Created a QA tool for contractors to evaluate bot's image operation results on thousands of images.

See bot's promotional post
See facial recognition model I trained

CryptoFace watchface for fitbit


An open-source Fitbit Sense/Versa 3 watchface to track crypto, stock, and forex prices using Yahoo Finance APIs. Customize up to 6 tickers to track with frequent updates. You may optionally refresh prices yourself with the "Refresh" button.

Rated 4.8 with 50+ ratings. 400+ crypto enthusiasts hitting Yahoo APIs more than 15k times per day for price refreshes. Logged more than 2 million total API hits since inception.

Developed the first Google Analytics 4 npm module specifically designed for fitbit projects. Simplifies the communication needed between the client-side watchface and the companion responsible for sending data to GA4.

See watchface code
See Google Analytics 4 module code

Yahoo Search

Development on scalable, ReactJs based optimized for mobile browsers utilized by hundreds of millions of users.

A/B testing of all new features, continuous delivery and strive for >90% code coverage.

Acquired ownership of Yahoo's native iOS Yahoo Search app and backends. Redesigned the app in the direction of contextual search, exploration, and personalization, which increased user engagement on the home screen by 3x.

Contributed to implementation and tracking to Mobile Web Search for Yahoo's partnership with, where Yahoo donated 10 cents per search in an effort to raise awareness and drive support for global issues.

© 2023, Nikolay Feldman (codeniko). All rights reserved