Sébastien Ballesteros
About me
I make change happen through software choices, hard work, collaboration, and attention to detail.
I am an experienced Web Software Engineer with a strong quantitative background (Ph.D. in mathematical modeling) and proven expertise in delivering well-architected solutions (from API design to complex React applications). I thrive in fast-paced environments working close to the creative process and in collaboration with product, research, and design teams.
Nothing is built on stone; all is built on sand, but we must build as if the sand were stone.
Experience
Senior Software Engineer (frontend), DuckDuckGo, remote (Santa Monica / San Francisco)
since 2020- Led the (incremental) rewrite of DuckDuckGo's search engine result page (and testing infrastructure) in React and drove cultural change through software choices, resulting in higher engineer productivity (as measured by Google's Goal Signal Metrics framework).
- Used those new foundations (and associated tooling) to drive the adoption of a design system.
- Led several web performance optimization projects (e.g., web vitals tracking and optimization) that resulted in a significant increase of the company's core engagement and revenue metrics.
- Led various fast-paced projects (using build/measure/learn cycles and working closely with product and design teams) that successfully improved the adoption and retention of DuckDuckGo's products (as measured by online controlled experiments and A/B testing).
- Identified key areas of improvement through the development of internal tools and applications to evaluate and monitor the performance of DuckDuckGo's search products.
- Drove the adoption of multiple new technologies (e.g., Next.js).
- Gained ownership and contributed to multiple areas of the code base (e.g., online controlled experiments framework, search engine result page, local search, browser extensions).
Technologies:
- JavaScript
- TypeScript
- React
- Next.js
- Storybook
- Testing library
- Node.js
- D3.js
- Browser extensions
- Webpack
- Grunt
- ClickHouse
- Grafana
- Elasticsearch
- SQL
- Jenkins
- HTML
- CSS
- RDFa
- JSON-LD
- Schema.org
- Bash
Senior Software Engineer (full-stack), Code for Science & Society, remote (Los Angeles)
2019–2020- Led the development and release of the frontend (React) and backend (Node.js / NoSQL Database) of a new product collecting reviews on preprints relevant to the Outbreak Science community, in close collaboration with product managers and design.
- Identified an opportunity to develop a browser extension for the product to better serve user needs at minimal cost and complexity (large code-reuse); and led its successful development and release.
Work samples: rapid-prereview (GitHub)
Technologies:
- JavaScript
- React
- Choo
- Node.js
- Browser extensions
- Webpack
- CouchDB
- PostgreSQL
- Redis
- Redisearch
- CircleCI
- HTML
- CSS
- RDFa
- JSON-LD
- Schema.org
- Bash
Technical Founder, sci.pe, Los Angeles - New York City
2014–2019- Earned acceptance to and completed Techstars NYC, Mozilla webFWD and Tigerlabs (Princeton) programs (the company was also known as Standard Analytics and science.ai).
- Helped major scholarly publishers to successfully transition from an XML/print-first workflow to an HTML/web-first one.
- Architected and built a complex React/Redux application (collaborative task completion, roles management, real-time updates, offline support, rich text editing, annotations, payments, first-class support for print).
- Designed and built a hypermedia API (and associated data model) based on schema.org actions.
- Architected and built a document transformation service (OOXML to HTML, image resizing, video transcoding).
- Built a CI/CD pipeline and deployed and monitored the application on AWS.
Work samples: science periodicals GitHub organization, Twitter threads (1, 2)
Technologies:
- JavaScript
- React
- Redux
- D3.js
- Node.js
- Webpack
- Browserify
- Zeromq
- CouchDB
- MongoDB
- PouchDB
- Redis
- Lucene / ElasticSearch
- AWS
- Docker
- CircleCI
- Stripe
- HTML
- CSS
- RDFa
- JSON-LD
- Schema.org
- Bash
- OOXML
- XML
- Python
Postdoctoral Fellow, Department of Ecology & Evolutionary Biology, Princeton University, Princeton, NJ
2011–2014Developed the infrastucture necessary to build a public library of mathematical and computational models of the dynamic processes of infectious disease spread and control, usable on demand from a web browser. The methods were successully adopted and applied by Doctors Without Borders and the London School of Hygiene & Tropical Medicine.
Work samples: GitHub repository, article on Spatial Transmission of 2009 Pandemic Influenza in the US
Technologies:
- C
- R
- Zeromq
- Python
- AWS
- JavaScript
- Node.js
- MongoDB
- D3.js
- Backbone.js
- jQuery
Postdoctoral Fellow, EPIWORK project, CMAF Centro de Matemática e Aplicações Fundamentais, Lisbon, Portugal
2010–2011Developed statistical and computational methods needed to achieve inference, prediction and predictability of disease spreading in complex techno-social systems.
Work samples: article on The role of weather on the relation between influenza and influenza-like illness
Technologies:
- C
- Zeromq
- Python
- R
- Django
- MySQL
Education
Ph.D. thesis in Ecology and Evolution, Laboratory Ecology and Evolution (UMR 7625); Universite Pierre et Marie Curie, Ecole Normale Supérieure, Paris, France - Awarded with distinction and special mention from the examination board
2006–2009My thesis focused on the development of statistical and computational methods to understand the processes driving outbreak dynamics of infectious diseases. Developements focused on influenza, dengue and HIV.
Technologies:
- Blackboard, pen & paper
- C
- R
- Python
Master’s Degree by research, Universities Paris 6 and Paris 11, AgroParisTech, Ecole Normale Supérieure, with honors (ranked first)
2005–2006Ecology, Biodiversity and Evolution, speciality Theoretical Ecology and Modeling.
France’s top post graduate engineering school for agronomy and life sciences (part of the ParisTech Grandes Ecoles).
Higher School Preparatory Classes (classes préparatoires aux grandes écoles), Lycée Jean-Baptiste-Say, Paris, France
2000–2003Intensive preparatory course with the main goal of training students for enrollment in one of the Grandes Ecoles.
Baccalauréat général série Scientifique (S) - Awarded with distinction, Paris, France
2000The S stream of the Baccalauréat prepares students for work in scientific fields.
Teaching
- Statistics (undergraduate students) at the Muséum National d’Histoire Naturelle and Princeton University.
- Scientific animation (popularisation works) in the Muséum National d’Histoire Naturelle. Those activities were based on interactive computer simulations that I developed for the Muséum.
Technological skills
- Programming
- JavaScript
- TypeScript
- C
- Python
- R
- Bash
- Web development
- React
- Redux
- Node.js
- Next.js
- XState
- D3.js
- Webpack
- Browserify
- HTML
- CSS
- RDFa
- JSON-LD
- RDF
- RDF Schema
- XML
- SPARQL
- OWL
- GraphQL
- Schema.org
- Payments
- Stripe
- E-commerce
- Shopify
- Databases
- CouchDB
- PouchDB
- MongoDB (certificate from 10gen)
- Fauna
- Firebase (Firestore)
- PostgreSQL
- Redis (certificate from redislab)
- LevelDB
- MySQL
- Lucene / ElasticSearch
- Cloud services
- AWS
- GCP
- Azure
- Vercel
- Continuous integration
- CircleCI
- Operating systems
- GNU/Linux
- OSX
- Docker
- Statistics
- R
- SAS
- WinBugs