Simon Flack, Developer in Jelenia Góra, Poland
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Simon Flack

Verified Expert  in Engineering

Bio

Simon is a senior full-stack engineer with experience building performant, resilient applications across web, mobile, and back-end systems. He's recently led cross-platform work at a healthcare startup, including native Bluetooth integrations, LLM prototyping, and automated CI/CD pipelines. Simon is passionate about developer experience, mentoring, and simplifying complex workflows with modern tools like TypeScript, XState, Postgres, and Django.

Portfolio

Arena Labs, Inc
HTML, JavaScript, CSS, HTML5, React, Python, Docker Compose, Tailwind CSS...
OnTrack Retail
Sass, Less, Git, Bash, MongoDB, Jest, Docker, XState, Redux, Webpack...
IG
Subversion (SVN), Raphaël, Handlebars, jQuery, JavaScript, Regular Expressions...

Experience

  • JavaScript - 10 years
  • React - 9 years
  • Node.js - 7 years
  • TypeScript - 6 years
  • Full-stack - 5 years
  • Playwright - 4 years
  • Mobile App Development - 4 years
  • Capacitor - 3 years

Availability

Full-time

Preferred Environment

XState, TypeScript, React, Next.js, PostgreSQL, REST APIs, Supabase, Large Language Models (LLMs), Capacitor, Node.js

The most amazing...

...win was replacing a slow public API with my own ingestion pipeline, cutting latency from 10 seconds to milliseconds and unblocking a major launch.

Work Experience

Senior Engineer

2021 - 2024
Arena Labs, Inc
  • Delivered a cross-platform healthcare app with Next.js and Capacitor, shipping to web, iOS, and Android stores, used daily by clinicians under pressure.
  • Designed and implemented a cross-platform Bluetooth plugin (Swift and Java) for biometric data capture, featuring an async API, robust error handling, and queuing—replacing unstable contractor code and enabling reliable device integration.
  • Mentored developers across the stack via code reviews, diagrams, and asynchronous videos. Boosted team velocity and raised the quality bar across PRs.
  • Automated CI/CD using GitHub Actions for releases, service status alerts, and in-app OTA updates, cutting manual effort and enabling same-day hotfixes.
  • Introduced internal in-app testing tools (log viewer, data reset, data inspectors, and state machine debugger) to accelerate QA and reduce support load.
  • Integrated Sentry Replay, Capgo, and analytics platforms to improve UX feedback, debug issues faster, and deliver OTA updates without app store delays.
  • Built reusable libraries and front-end patterns to reduce duplication and technical debt, enabling faster iteration while maintaining consistency.
  • Collaborated closely with design, product, and QA to scope features, validate delivery feasibility, and adjust priorities when needed.
Technologies: HTML, JavaScript, CSS, HTML5, React, Python, Docker Compose, Tailwind CSS, Ionic, Technical Leadership, PostgreSQL, API Integration, Email Automation, Chatbots, Mobile Development, Front-end, User Experience (UX), User Interface (UI), Full-stack Development, Back-end, Infrastructure as Code (IaC), Scraping, Supabase, Webhooks, REST APIs, Databases, Deployment, OpenAI API, Puppeteer, React Testing Library, Vite, WCAG, Data Visualization, Capacitor, Bluetooth, XState, Playwright, CI/CD Pipelines, OpenAI, Large Language Models (LLMs), React Query, Messaging, Mobile App Development, Encryption, Single-page Applications (SPAs), Solution Architecture, DevOps

Senior Front-end Developer

2015 - 2021
OnTrack Retail
  • Built and maintained a high-traffic retail ticketing platform used by five UK rail operators, handling £500,000+ in daily transactions.
  • Replaced a slow 3rd-party timetable API with a real-time internal service using MongoDB and Node.js, reducing response time from 10 seconds to sub-second.
  • Developed and shipped multiple government-compliant delay compensation portals across Southeastern and GTR under tight deadlines.
  • Led a major Webpack system rewrite. Cut CI build times in half, improved developer velocity, and modernized the toolchain.
  • Extracted reusable functionality from the monolith to enable faster product spin-up for new rail clients - paving the way for modular growth.
  • Created a self-service ticket refund system, improving customer autonomy and reducing support overhead.
  • Mentored junior developers remotely - shared domain knowledge, introduced better testing practices, and improved PR quality.
Technologies: Sass, Less, Git, Bash, MongoDB, Jest, Docker, XState, Redux, Webpack, TypeScript, AngularJS, React, Node.js, Test-driven Development (TDD), API Design, JavaScript, Express.js, Redis, Regular Expressions, Webpack 4, Gulp, NGINX, Visual Studio Code (VS Code), Chrome, HTML, SQL, CSS, Debugging, MySQLdb, Handlebars, Accessibility, HTML5, Architecture, Web Development, REST, Google Analytics, Integration, Braintree SDK, PayPal, Web Scraping, Next.js, UI Testing, Algorithms, Full-stack, MySQL, Webpack 3, SSH, Webpack 2, APIs, Capacitor, Mobile Apps, Docker Compose, Amazon Web Services (AWS), API Integration, Azure, Front-end, User Experience (UX), User Interface (UI), Full-stack Development, Back-end, Infrastructure as Code (IaC), Data Scraping, Scraping, Google Tag Manager, REST APIs, Databases, Puppeteer, Material UI, React Testing Library, Vite, WCAG, Single-page Applications (SPAs), Solution Architecture, DevOps

Senior Front-end Developer

2014 - 2015
IG
  • Developed an interactive UI for investors to filter thousands of markets using fundamentals and custom criteria - optimized for desktop and tablet.
  • Refactored server-rendered pages to share front-end templates across views - improved maintainability and reduced duplication.
  • Conducted screening and in-person technical interviews for junior and senior developer roles - helped grow and shape the team.
  • Initiated weekly tech meetups to foster cross-team learning, improve collaboration, and share engineering best practices.
  • Collaborated with iOS and Android teams to debug and fix issues in embedded WebViews - improved cross-platform reliability.
  • Built dynamic SVG-based data visualizations using Raphaël - enhanced clarity and usability for high-volume financial data tools.
Technologies: Subversion (SVN), Raphaël, Handlebars, jQuery, JavaScript, Regular Expressions, Gulp, Chrome, HTML, Node.js, CSS, Debugging, Bash, HTML5, Web Development, Integration, Algorithms, Grunt, SSH, Capacitor, Mobile Apps, Content Management Systems (CMS), Cloud Firestore, Data Visualization, D3.js

Front-end Developer

2010 - 2014
BBC
  • Developed the front end for custom CMS document repository and filtering.
  • Implemented instant and scheduled publishing interfaces according to design.
  • Translated business requirements into BDD tests and built monitoring tools to highlight failing tests.
  • Supported legacy CMS platform and created migration tools for the new platform.
  • Created a visual "segments editor" for media publishers to generate thumbnails and short clips as part of a media publishing pipeline.
  • Built a schedule builder to create timetables and assign program metadata to multiple live streams as part of the London 2012 Olympics programming.
  • Created and maintained plugins for a custom publishing workflow.
  • Built a multi-file upload component capable of handling very large media files, supporting resumes, and reporting back transcode status.
Technologies: Sass, Less, Behat, PHPUnit, Jasmine, Zend Framework, PHP, jQuery, Backbone.js, JavaScript, Perl, Regular Expressions, Gulp, Chrome, HTML, CSS, Debugging, Bash, HTML5, Web Development, REST, Integration, UI Testing, Full-stack, Apache2, Behavior-driven Development (BDD), Grunt, SSH, RSync, APIs, Docker Compose, Content Management Systems (CMS), REST APIs, Databases, Deployment, Solution Architecture

Software Engineer

2002 - 2010
BBC
  • Worked with production teams to develop interactive websites using custom tools.
  • Designed and developed a desktop CMS application with an Oracle-backed SOAP server for managing, transforming, and publishing vast repositories of XML content.
  • Developed an FTP interface to simplify bulk import and export of content.
  • Published the organization's first open-source contributions and ported the Document and View framework in wxWidgets to wxPerl.
  • Embedded Internet Explorer for in-editor CSS-based preview and full XSLT preview of the content.
  • Implemented common editor functions such as in-editor find and replace, cross-repository find and replace, and spell-check.
  • Demoed new features on a monthly basis and incorporated user feedback into future releases.
  • Completed a Bayesian analysis of 45,000 articles for categorization in the People's War Archive.
  • Recovered data from Laserdisc in legacy format for the BBC Domesday Reloaded project.
Technologies: OLE, ODBC, Oracle, XSLT, XML, wxWidgets, CSS, HTML, Perl, Regular Expressions, Debugging, MySQLdb, HTML5, Architecture, Web Development, Web Scraping, UI Testing, Full-stack, Apache2, SSH, RSync, APIs, Content Management Systems (CMS), Email Parsing, Email Automation, Full-stack Development, Back-end, Databases, Solution Architecture

Experience

Booking Engine

https://ticket.greatnorthernrail.com
A React-based train ticket eCommerce app for planning journeys, purchasing tickets, and processing refunds. The app is used by five train operators, supports tens of thousands of visitors, and has several hundred thousand GBP in transactions on a daily basis.

Delay Repay Compensation

https://delayrepay.southeasternrailway.co.uk/
A statically rendered React app for customers to apply for delay repay compensation after experiencing delays to their journey of over 15 minutes. The application is streamlined for returning customers and guides users through the required information. The application logic is modeled with statecharts using XState for improved flexibility and maintainability.

Darwin

A MongoDB-backed API for querying train timetables to find details of trains users traveled on as part of their delay repay claim application. A scheduler pulls the daily timetable XML from Amazon S3 every morning and ingests the data after processing it so it can be queried quickly and efficiently.

Market Screener

https://www.ig.com/uk/markets-stock-screener?country=GB,US
A tool for investors to create, save, and edit custom filters for investment opportunities. Written with Vanilla JS, SVG, and a custom in-house framework. It was designed to work well on desktops and tablet devices.

FLiP - Factual and Learning Interactive Publisher

A desktop and server application for editing and publishing large repositories of XML. Written in wxPerl, using wxWidgets for the UI, and interfacing with LDAP for authentication and OLE for embedding Internet Explorer. SciTE. Used SOAP and FTP as primary protocols, and supported multiple repository back ends including filesystem and Oracle.

Arena Strive – Mobile Health App

https://arenalabs.co
Led the development of a cross-platform mobile app supporting clinician stress and recovery, built with Capacitor and React. Designed a Bluetooth plugin in Swift/Java for biometric data sync, added async APIs, queueing, and error handling. Built in-app developer tools and debug workflows to support internal testing and QA.

Web Portal for Coach-guided Recovery (Arena Strive)

https://arenalabs.co
Built a companion web dashboard for coaches to manage user journeys and review biometric insights. Integrated with internal APIs and analytics tools. Developed automated test flows using Playwright and deployed to Vercel.

SubScout – AI-powered Subscription Tracker (Prototype)

https://subscout.app
Designed and built an MVP for a privacy-first subscription tracker. The app extracts and classifies subscription data from user-forwarded emails, using LLM prompts and regex pipelines. It was built with Supabase, PostgreSQL, and React Native. It emphasizes local-first architecture and user value perception over raw usage metrics.

Wellbeing Tracker & Support Bot for Grief Community

Built a custom Discord bot to help community members share how they’re doing and track their well-being over time. Designed with empathy and minimal friction to support emotional expression and solidarity. Also contributed to a related creative art project focused on remembrance and healing.

Skills

Libraries/APIs

Node.js, React, jQuery, REST APIs, OpenAI API, Puppeteer, React Testing Library, Playwright, React Query, Stripe, Backbone.js, D3.js, Handlebars, Raphaël, wxWidgets, ODBC

Tools

Git, Webpack 4, Webpack 3, Capacitor, Webpack, Gulp, Grunt, Webpack 2, Braintree SDK, NGINX, Subversion (SVN), Behat, Google Analytics, Docker Compose, GitLab CI/CD

Languages

JavaScript, Perl, TypeScript, CSS, HTML, HTML5, Less, Sass, XML, PHP, SQL, Bash, XSLT, Python, Objective-C, Swift, Java

Frameworks

Jest, Express.js, Next.js, Tailwind CSS, NestJS, AngularJS, React Native, Ionic, Cypress, Material UI, Chrome, Redux, Zend Framework, Jasmine, PHPUnit

Paradigms

Test-driven Development (TDD), REST, Mobile Development, Behavior-driven Development (BDD), DevOps, Offline-first Development, UX Design

Platforms

Amazon Web Services (AWS), Vercel, Linux, Docker, Apache2, Android, iOS, Firefox, Oracle, Visual Studio Code (VS Code), Azure

Storage

Amazon S3 (AWS S3), Databases, MySQL, MySQLdb, MongoDB, PostgreSQL, Cloud Firestore, Redis

Other

Regular Expressions, API Design, Debugging, Full-stack, Web Development, Architecture, Web Scraping, APIs, Content Management Systems (CMS), Technical Leadership, Software Architecture, API Integration, Email Automation, Front-end, User Interface (UI), Full-stack Development, Back-end, Data Scraping, Scraping, Data Enrichment, Webhooks, Deployment, Vite, WCAG, Cursor AI, Messaging, Mobile App Development, Single-page Applications (SPAs), Solution Architecture, UI Testing, Algorithms, RSync, SSH, XState, Accessibility, Integration, PayPal, Large Language Models (LLMs), iPad, ChatGPT API, OpenAI, Bluetooth, Email Parsing, Chatbots, User Experience (UX), Infrastructure as Code (IaC), Supabase, Google Tag Manager, Data Visualization, Subscriptions, Encryption, AI Integration, OLE, Mobile Apps, Videos, Zustand, CI/CD Pipelines, GitHub Actions, Prototyping, MVP Design, Discord, Discord Bots, Community, Creative Tech

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