William Hein
Verified Expert in Engineering
Software Developer
Aarhus, Denmark
Toptal member since June 3, 2026
William builds software for the hard cases, including real-time trading infrastructure, multi-agent AI automation, and B2B sales-intelligence dashboards. He has spent more than five years shipping production code in TypeScript, Go, Python, and several other languages, building autonomous systems that run against unreliable real-world data. William takes a project from the first commit through production and replies fast.
Portfolio
Experience
- SQL - 8 years
- JavaScript - 8 years
- Git - 7 years
- Python - 6 years
- Node.js - 6 years
- TypeScript - 6 years
- PHP - 5 years
- Go - 4 years
Preferred Environment
MacOS, Visual Studio Code (VS Code), Git, Docker, Podman, PostgreSQL, Cloudflare, Amazon Web Services (AWS), TypeScript, Python, Code Auditing, Code Refactoring, Performance Optimization, Artificial Intelligence (AI), Documentation, GitHub
The most amazing...
...solution I've built is sentient-evolve AI agents that evolve a trading strategy, write the code, and fix their own compile errors unattended.
Work Experience
Founder and Lead Developer
Self-employed
- Built the Murph sales intelligence dashboard leveraging Next.js, TypeScript, and PostgreSQL from the initial commit, enhancing LinkedIn outreach SaaS through ICP-driven commenting.
- Architected a multi-agent system that autonomously evolves trading algorithms.
- Engineered a feedback loop where specialized AI agents analyze performance, generate code improvements, and self-correct compilation errors in isolated Docker containers.
- Built iq-data-server in Go to ingest real-time WebSocket streams from 7+ major exchanges, including Binance, Bybit, and Coinbase.
- Hardened the high-frequency ingest path by eliminating race conditions and head-of-line blocking, bounding unbounded tracker growth, and removing unsafe upsert patterns.
- Enhanced a production Flutter iOS and Android app, built a companion MusicFix web utilizing Next.js with 300+ files from scratch, and developed a Firebase back end with strict Firestore security rules.
- Engineered a distributed scraping platform with a producer-consumer architecture and worker threads handling high-concurrency ingestion from Ticketmaster and other vendors.
- Developed rolly-extension, a Chrome extension for automated trading, implementing human-emulation algorithms to bypass modern bot detection systems.
- Implemented human-emulation algorithms such as randomized event dispatching and heuristic DOM recovery to bypass modern bot detection systems.
Technical Support
True Energy A/S
- Provided technical support for app-related issues, acting as a bridge between users and the engineering team to resolve bugs in the EV charging platform.
- Resolved technical issues for clients, ensuring high levels of customer satisfaction.
- Implemented process improvements that enhanced response times for technical inquiries.
Developer
XSpectar
- Built xspectar-nft-daemon, a local WebSocket server for subscribing to the XRP Ledger stream, enabling real-time updates for NFT transactions.
- Implemented a verification system for user token holdings, ensuring secure and verified participation.
- Processed live transactions to verify NFT ownership and instantly update user roles across Discord and internal databases, enhancing user experience.
Experience
Orpheus Festudvalget — Ticketing & Entry Platform
https://orpheus.dkThe backend is a TypeScript Express REST API backed by MariaDB, with JWT auth, invite-based registration, events, ticket types, and orders.
The system issues tickets as generated PDFs (Puppeteer) and delivers them by email, then validates entry through QR codes scanned in a dedicated admin panel that tracks attendance in real time.
To keep design iteration fast, I wrote a custom "Webflow Compiler" build pipeline that takes the static Webflow export and rewires it into pages driven by the live API, so visual updates ship without touching backend code. I later modernized the whole stack into a containerized Docker/Podman deployment and hardened the checkout flow with idempotency keys and session fixes.
MusicFix — Cross-Platform App & Web Platform
https://musicfix.dkI authored that backend myself: strict Firestore security rules, Cloud Functions, and Stripe payments.
Separately, I built the companion web platform, musicfix-web, from scratch in Next.js and TypeScript, with Tailwind, Radix UI, TanStack Query, geo-based search, internationalization, and the same Stripe and Firebase integration. The result is one app and one web surface sharing a single backend.
Battery Management Tool for Apple Silicon Macs
https://github.com/will2022/ChargeControlTypeScript Bridge Between Discord and Minecraft
https://github.com/will2022/OverflowBridgeEducation
Higher Technical Examination in Communication/IT A & Programming B
Tekniske Gymnasium - Vejle, Denmark
Skills
Libraries/APIs
Node.js, React, jQuery, REST APIs, React Router, React Query, NetSuite API, SQLAlchemy, Playwright, Puppeteer, Three.js, Stripe, Socket.IO, WordPress API, Vue, OpenAPI, Chart.js, Pydantic, Binance API
Tools
Git, GitHub, Prettier, Visual Studio, Amazon EKS, RabbitMQ, Claude, Claude Code, AWS Key Management Service (KMS), AWS IAM, Amazon Elastic Container Registry (ECR), Amazon ElastiCache, Flyway, n8n, Windsurf
Languages
TypeScript, Python, Go, PHP, SQL, JavaScript, HTML5, CSS, HTML, Shopify Liquid, Dart, Bash, Swift, Java, SuiteScript 1, SuiteScript 2, Snowflake, C++, C#
Frameworks
Django, Flask, Laravel, CodeIgniter, Symfony, Next.js, Express.js, Flutter, React Native, OAuth 2, Redux, Unity, LangGraph, Angular, Spring AI, Spring, Spring Boot, gRPC, Swagger, Ghidra, Electron
Paradigms
Code Refactoring, Visual Design, UI Design, Microservices Architecture, Role-based Access Control (RBAC), Microfrontends, Automation, Fast Healthcare Interoperability Resources (FHIR), Model Context Protocol (MCP)
Platforms
MacOS, Visual Studio Code (VS Code), Windows, Linux, Azure, Shopify, Docker, Amazon Web Services (AWS), Firebase, Netlify, Android, iOS, Kubernetes, Google Cloud Platform (GCP), WordPress, Databricks, Apache Kafka, Oracle, Vercel, ARCore, Mixpanel, Klaviyo
Storage
NoSQL, MariaDB, MongoDB, Database Migration, JSON, PostgreSQL, MySQL, Amazon S3 (AWS S3), Redis, Amazon Aurora
Other
FastAPI, Scraping, Full-stack, Information Technology, Front-end, Full-stack Development, Google, Programming, Software Architecture, API Integration, Back-end, Code Auditing, Performance Optimization, Cursor AI, Artificial Intelligence (AI), Architecture, Design Systems, Front-end Architecture, Documentation, APIs, Webhooks, Third-party API orchestration with webhooks/polling, NetSuite, NetSuite CRM, User Interface (UI), User Experience (UX), Workflows, Application Modernization, Document Processing, PDF, Figma to Shopify, Podman, Cloudflare, ESLint, Non-fungible Tokens (NFT), Crypto, WebSockets, GRAPH, Discord, Payment APIs, Security, 3D Maps, Amazon RDS, Amazon Bedrock, Technical Leadership, WordPress Plugins, Data Science, Data Engineering, Geospatial Data, Machine Learning, Machine Learning Operations (MLOps), AI Integration, Prompt Engineering, Supabase, AI Agents, AI Automation, Large Language Models (LLMs), OAuth, OpenAI, Video Processing, Computer Vision, Intuit QuickBooks, Agentic AI, Multi-agent Systems, User Flows, AI Tools, Integration, HL7, SQL Server, LangChain, eCommerce UX, Trading, Chargebee
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