Dan Castellon
Senior Software Engineer at Microsoft
Ayer, Massachusetts, United States
Summary
🤩
Rockstar🎓
Top SchoolDan Castellon is a senior software engineer with over 15 years of hands-on experience building scalable, high-performance web applications and services. He excels at architecting clean, maintainable full-stack systems—from backend sitemap generators and job orchestration to polished React front-ends—and has driven production features at scale for teams at Microsoft, Optum, and Reaction Commerce. At Microsoft he led end-to-end features for Whiteboard and M365 Copilot integrations, contributed early LLM-powered prototypes and evaluation tooling, and helped migrate Copilot workflows to new back-end platforms. An active contributor to open-source commerce projects, he has implemented both front-end component refactors and backend sitemap automation for Reaction Commerce’s repos. Based in Ayer, Massachusetts, he combines deep technical breadth (Node, Go, TypeScript, React, GraphQL, Docker/K8s) with mentoring and product-focused engineering that speeds delivery of complex features.
10 years of coding experience
12 years of employment as a software developer
High School, Computer Programming and Web Development, Honor Student, High School, Computer Programming and Web Development, Honor Student at Assabet Valley Technical School
English
Stackoverflow
11reputation
154reached
1answer
0questions
Github Skills (25)
javascript10
ecommerce10
nextjs10
wpgraphql10
wordpress-graphql10
graphql10
nodejs10
apollo10
react10
mongodb-database9
meteor9
mongodb9
testing8
react-ssr8
headlessui7
Programming languages (5)
Github contributions (5)
reactioncommerce/reaction
Jul 2018 - Mar 2019
Mailchimp Open Commerce is an API-first, headless commerce platform built using Node.js, React, GraphQL. Deployed via Docker and Kubernetes.
Role in this project:
Back-end Developer
Back-end DeveloperContributions:337 commits, 32 PRs, 191 pushes in 8 months
Contributions summary:Dan primarily contributed to the "reactioncommerce/reaction" project by implementing features related to the sitemap generator. These features included generating sitemaps on demand, adding the sitemap generation button to shop settings, implementing routes to automatically serve generated sitemap files, creating a job that automatically regenerates sitemaps periodically, and improving its performance.
ecommerceapi-firstshopping-cartreact-jsshop
reactioncommerce/example-storefront
Aug 2018 - Feb 2019
Example Storefront is Reaction Commerce’s headless ecommerce storefront - Next.js, GraphQL, React. Built using Apollo Client and the commerce-focused React UI components provided in the Storefront Component Library (reactioncommerce/reaction-component-library). It connects with Reaction backend with the GraphQL API.
Role in this project:Front-end Developer
Front-end DeveloperContributions:18 commits, 3 PRs, 11 pushes in 5 months
Contributions summary:Dan primarily focused on updating and porting components from the `reactioncommerce/reaction-component-library` to the example storefront. This involved refactoring code, removing unused dependencies, and integrating the `CatalogGrid` component. They also addressed test failures related to these changes and updated the `ProductGrid` component. Further contributions included fixing eslint issues, removing an unneeded URL, and fixing merge conflicts.
next-jsecommerceheadless-ecommerceshopping-cartshop
Find and Hire Top DevelopersWe’ve analyzed the programming source code of over 60 million software developers on GitHub and scored them by 50,000 skills. Sign-up on Prog,AI to search for software developers.