Senior Full-Stack Engineer (React, Node, AWS)

Allan Castellanos

Senior Software Engineer / Mexico City

Results-driven and highly skilled Full-stack Software Engineer with a proven track record of success spanning 9 years in the industry. Adept at collaborating within multicultural teams on a global scale, with experience contributing to the success of major corporations as well as innovative startups. Experience:

Senior Software Engineer Signify (2024 - 2026)

Worked as a Senior Software Engineer at Signify, a consulting firm specializing in bespoke software solutions for diverse clients, where I contributed to multiple high-impact projects with responsibilities spanning from architecture design to full-stack development.

NerdWallet (Financial Technology Platform)

• Collaborated continuously on feature enhancements aimed at improving user experience and conversion rates.

• Implemented the unit test testing strategy for the codebase, defining scalable testing practices for the project, increasing coverage React components, Redux logic, and shared utilities to improve reliability and reduce regressions.

• Developed reusable React and Next.js components with TypeScript and managed complex state using Redux.

• Optimized styling and responsiveness with TailwindCSS, integrating seamlessly with PHP and WordPress-driven backends.

• Ensured high availability and performance through AWS CDN (CloudFront), DynamoDB, Amplify, Cognito, and GCP services, automating deployments with Jenkins.

• Developed API’s work using Node + NestJs, documentation using Swagger and versioning Finix (Payments Integration Platform)

• Built and delivered new features across React, TypeScript, Node.js, and Python, supporting payment platform capabilities and internal product initiatives.

• Improved long-term maintainability by reducing technical debt, refactoring legacy code paths, and driving cleaner engineering patterns across the codebase.

• Led the implementation of the automated testing strategy, raising coverage to 90% and improving release confidence through stronger unit, integration, and CI validation.

• Supported production reliability through on-call incident response, including live troubleshooting, root cause analysis, and follow-up fixes to prevent regressions.

• Worked directly with Product Managers and Designers to shape requirements, evaluate tradeoffs, and execute features from discovery through release.

• Mentored teammates through PR reviews, implementation feedback, and hands-on technical support, reinforcing quality standards and team growth.

Senior Software Engineer PayPal (2021 - 2024)

As a Senior Software Engineer in PayPal's "Wallet" micro-domain, I delivered full-stack solutions to enhance the PayPal Wallet web experience, focusing on scalability, performance, and user impact.

• Developed key features using React, Next.js, TypeScript, Java, Node.js, and Python, contributing to components used by millions.

• First 3 months I was involved in a project to increase codebase coverage from 20% to 85%

• Took ownership of SDLC tasks: planning, coding, testing, code reviews, and deployment.

• Collaborated with cross-functional teams to align features with business goals.

• Led incident resolution, improved legacy codebases, and optimized CI/CD pipelines with Jenkins.

• Mentored junior engineers and contributed to technical roadmap planning.

• Developed API’s work using Node + NestJs, documentation using Swagger and versioning Consistently brought senior-level leadership to complex engineering efforts in a high-impact fintech environment. Lead Software Engineer Konfio / Sr Pago (2016 - 2021) Directly collaborated with the CEO and marketing team to craft user-centric experiences for the company’s e-commerce, product, and SDK websites. As a technical lead, I guided a team of engineers, copywriters, and designers, architecting and building digital products from scratch.

Tech Stack:

Front-End: React, Next.js, Redux, Remix, Angular, Jest, Enzyme, TypeScript, JavaScript, jQuery, HTML5, CSS3, SASS, LESS, Styled Components, Bootstrap, Tailwind, MUI, NextAuth, Formik, Storybook, Figma, Adobe XD, Liquid.

Back-End: Node.js, NestJs, PHP, Python, Apollo, Express, GraphQL, Typescript, Design Patterns, Data Structures, Big O Notation, OOP.

Testing: Jest, React Testing Library, Enzyme, Cypress, Playwright, Vitest, Mocha, Chai, Jasmine, Puppeteer, MSW, Unit Testing, Integration Testing, End-to-End Testing. Cloud: OpenAI, AWS (Serverless, Amplify, Lambda, S3, DynamoDB, CloudFront, SES, EC2, Route 53, Cognito).

Databases: SQL, PostgreSQL, MongoDB, DynamoDB, Redis, Prisma. CI/CD: Jenkins, TeamCity, GitHub Actions, Terraform, SonarQube. Tools: GitHub, GitLab, Jira, Slack, Confluence, SCRUM. CMS: Shopify, WordPress, WooCommerce, Magento, Webflow. Graphic Design: Photoshop, Illustrator, Premiere, Final Cut. Music Production: ProTools, Cubase, Logic, Live.

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