Hassan Khattak
Verified Expert in Engineering
Full-stack Engineer and Developer
Lahore, Pakistan
Toptal member since July 7, 2026
Hassan is a senior full-stack engineer with 7+ years of experience shipping complex, user-facing SaaS products, from architecture and implementation through deployment, infrastructure, and production monitoring. His core expertise is in Ruby on Rails, React, and Next.js, complemented by hands-on production experience with Python and the MERN stack. Hassan is comfortable taking ownership of technical challenges from system design through delivery and ongoing operational support.
Portfolio
Experience
- MERN Stack - 6 years
- Python - 6 years
- Node.js - 6 years
- JavaScript - 6 years
- React - 5 years
- Artificial Intelligence (AI) - 4 years
- Large Language Models (LLMs) - 3 years
- Ruby on Rails (RoR) - 3 years
Work Experience
Senior Software Engineer, Founding Team
AI Recruitment Platform
- Joined as a founding engineer and took the product from zero to a live, high-concurrency SaaS platform approved on both the Apple App Store and Google Play.
- Built the core AI matching engine using OpenAI and LLMs, powering candidate-job ranking and recommendations that define the platform's core value proposition.
- Engineered an Elasticsearch-based search system with relevance tuning across job listings and candidate profiles, built to handle concurrent load at scale.
- Owned authentication and onboarding using OAuth 2.0, JWT, and Devise, implementing role-based access control across web and mobile applications.
- Designed a credit-based billing and workflow automation system on Stripe, including plan management, automated triggers, usage metering, and renewal workflows.
- Managed AWS infrastructure, including PostgreSQL clusters, Sidekiq background processing, automated backups, cluster migrations, and horizontal scaling.
- Introduced feature flags for gradual, zero-downtime rollouts.
- Built analytics dashboards tracking acquisition funnels, feature adoption, and business metrics.
- Grew and mentored a team of 3–5 engineers while partnering directly with the CEO to define product requirements and shape the roadmap.
Senior Software Engineer
Devsinc
- Delivered multiple client-facing SaaS products end to end using Ruby on Rails, React, TypeScript, PostgreSQL, and MySQL.
- Built and maintained an observability stack using OpenTelemetry, Prometheus, and Grafana, enabling distributed tracing, metrics collection, and structured logging through a custom log formatting and filtering pipeline.
- Designed a multi-tenant, role-based permission and workflow automation system with fine-grained access control and automated event triggers.
- Managed Kubernetes infrastructure across multi-service deployments, cluster migrations, and performance tuning for high availability.
- Scaled Stripe payment infrastructure across multiple platforms, handling thousands of concurrent transactions monthly via Sidekiq-powered async workflows.
- Integrated Shopify APIs and webhooks for eCommerce clients and shipped React and Tailwind CSS dashboards tracking conversion and store performance.
- Implemented event instrumentation, feature flags, and A/B testing for data-driven iteration.
- Set up CI/CD pipelines with AWS and Docker, maintained RSpec test suites, and mentored junior engineers.
Software Engineer
Erstech
- Developed customer-facing Rails apps with JavaScript and jQuery, growing test coverage by approximately 25% via RSpec, Cucumber, and Jest, and directly cut production incidents.
- Architected and optimized RESTful APIs on PostgreSQL and MySQL with object caching and query tuning that improved response times.
- Collaborated closely with product and business teams across the full development lifecycle in an Agile environment.
Junior Software Engineer
WorldCall Telecom Limited (WTL)
- Built responsive web and mobile applications with Ruby on Rails, React, and React Native, applying strong fundamentals in component architecture and state management.
- Integrated 3rd-party APIs and SDKs and adopted Git and GitHub workflows and Agile sprint cycles.
- Collaborated with senior engineers and QA to debug production issues, improving feature stability and reducing post-release bug reports.
Project History
ImageRelay Platform
http://image-relay-api.readme.ioAI Recruitment Platform
http://jobzhr.comBioMark
https://www.biomarking.com/I worked on building and enhancing the platform with a focus on scalable back-end services, secure healthcare data management, API development, and seamless communication between patient and doctor-facing applications.
Education
Bachelor's Degree in Computer Software Engineering
Superior University - Lahore, Pakistan
Skills
Libraries/APIs
Stripe, React, jQuery, Node.js, Playwright, PostgREST, Claude API, REST APIs, Salesforce API, OpenAI API, Twilio API, FFmpeg, OpenCV, PyTorch, TensorFlow, Pydantic, Google Maps, React Router, Google Maps API, Stripe API, Vue, Mapbox API, React Hook Form, React Testing Library, API Development, Liquid, Steam Integration, Steam Web API, Azure API Management, WebRTC, Protobuf, Auth, Graph API, PiLLoW, PowerPoint API, GraphQL API, Entity Framework, Pandas, Vue 3, Drizzle, Handlebars, Devise, Sidekiq
Tools
GitHub, Claude Code, Claude, Azure OpenAI Service, Terraform, ChatGPT, Git, Amazon Elastic Container Service (ECS), Acumatica, GIS, Bitbucket, Expo, Vitest, Google Analytics, Whisper, Firebase Authentication, Zapier, Zoom, Figma, Adobe CC, Adobe, RabbitMQ, Pytest, Google Sheets, Microsoft Excel, Amazon CloudWatch, GitLab CI/CD, n8n, Azure Application Insights, Microsoft Power Pages, SAP Remote Function Call (RFC), AWS IAM, Codex, Shadcn, CAD, MongoDB Atlas, Odoo, Claude Agent SDK, Microsoft Power Apps, AI Prompts, GraphRAG, Prisma, Amazon EKS, Celery, Drizzle ORM, Visual Studio, Visual Studio App Center, Grafana, RSpec, Cucumber, Jira, Vagrant
Languages
TypeScript, JavaScript, CSS, Python, Artificial Intelligence Markup Language (AIML), HTML, Clojure, SQL, Ruby, GraphQL, Go, Java, PHP, HTML5, Rust, C++, Liquid Template, Shopify Liquid, Bash, Kotlin, C#, Google Apps Script, SPARQL, CSS3, SCSS
Frameworks
Next.js, React Native, Ruby on Rails (RoR), Django, Express.js, Tailwind CSS, LangGraph, ClojureScript, OAuth 2, MediaPipe, Flask, Agentic Frameworks, NestJS, Laravel, Angular, Symfony, Flutter, Ruby on Rails 7, Streamlit, Material UI, Selenium, gRPC, Redux, Ray, Fastify, Payload CMS, .NET, LlamaIndex, Nuxt 3, Nuxt.js, Serverless Framework, JSON Web Tokens (JWT), Jest
Paradigms
UX Design, Agile UX, Testing, Real-time Systems, Automation, Event-driven Architecture, Functional Programming, Microservices, Model Context Protocol (MCP), Back-end Architecture, Role-based Access Control (RBAC), Marketplace Platforms, Mobile Development, Database Design, DevOps, Automated Testing, Search Engine Optimization (SEO), ETL, UI Design, Unit Testing, API Architecture, Object-oriented Design (OOD), HIPAA Compliance, Microfrontends, Synthetic Data Generation, High-performance Computing (HPC), Azure DevOps, Web Application Architecture, Clean Code, Continuous Integration (CI), REST, Best Practices, Maintainability, ACID, Service-oriented Architecture (SOA), Application Architecture, Responsive Layout, Agile
Platforms
Amazon Web Services (AWS), Google Cloud Platform (GCP), Vercel, Azure, Azure Functions, Microsoft Power Automate, SharePoint, WordPress, Twilio, NVIDIA CUDA, Databricks, Apache Kafka, Heroku, Clerk, Sitecore Experience Manager Cloud (XM Cloud), Cloud Native, Netlify, Firebase, Mapbox, iOS, Kajabi, LangSmith, Shopify, Web, Harness, Mobile, Telnyx, AWS Lambda, Windows, Android, WooCommerce, Microsoft Power Platform, Replit, Grok, DigitalOcean, Linux, BigCommerce, Visual Studio Code (VS Code), AWS IoT, Docker, Kubernetes
Storage
PostgreSQL, MongoDB, Google Cloud, Databases, Database Management, Azure SQL, Data Pipelines, Object Storage, JSON, Amazon S3 (AWS S3), Microsoft Entra ID, ClickHouse, Data Integration, Amazon DynamoDB, PL/SQL Developer, Database Architecture, Google Cloud SQL, Relational Databases, Elasticsearch, Redis, MySQL
Industry Expertise
Healthcare, Project Management, Accounting, Web Design
Other
Large Language Models (LLMs), Shopify APIs, CI/CD Pipelines, Software Development, MERN Stack, Artificial Intelligence (AI), APIs, stimulus.js, Full-stack, AI Copilots, API Integration, Agentic RAG Systems, CRM, Large Language Model Operations (LLMOps), Fintech, Minimum Viable Product (MVP), Prompt Engineering, User Experience (UX), Back-end, Coding, Technical Leadership, Agentic AI, Agentic AI Systems, Agentic Workflow Design, Enterprise Resource Planning (ERP), LangChain, Optical Character Recognition (OCR), Image Recognition, eCommerce, Architecture, AI Agents, Full-stack Development, Multi-agent Orchestration, Supabase, Workflow, Multi-agent Systems, Workflows, Front-end, Client Communication, Customer Support, Troubleshooting, Web Development, DNS, User Interface (UI), Web Scraping, Lovable, Progressive Web Applications (PWAs), Solution Architecture, Integration, Third-party Integration, Charts, Data Engineering, Data Visualization, Data Analytics, HIPAA, HIPAA Electronic Data Interchange (EDI), SOC 2, Authentication, Cloud Storage, Software Architecture, ARM, Embedded Systems, Sensors & Actuators, State Machines, LLM Integration, Workflow Automation, Communication, AI Agent Orchestration, Machine Learning, Cloud Infrastructure, Life Science, Azure AI Document Intelligence, Supabase Auth, Agentic Coding, RAG Pipelines, Retrieval-augmented Generation (RAG), Temporal, FastAPI, Amazon Bedrock AgentCore, Terraform Cloud, Product Management, CTO, Cloud Architecture, Compliance, Data Security, SaaS, Lead Generation, Scraping, Data Processing, Distributed Systems, RAG Architecture, RAG Systems, Scalability, Bun, Debugging, Pinecone, Workflow Automation & System Integration, Advisory, Consulting, IT Consulting, SMS, Cloudflare, Back-end Development, Webhooks, AI-assisted Development, Figma to React, Marketplaces, Cursor AI, Integrations, Infrastructure, Robotics, AI Integration, Firebase Cloud Functions, Technical Architecture, Concurrency, Financial Services, Leadership, Team Management, Mentorship, Payments, Computer Vision, Data Labeling, Feature Engineering, Key Performance Indicators (KPIs), Object Detection, Pose Estimation, Video Analysis, Front-end Development, Event-driven Systems, AI Voice Agents, Mobile App Development, Mobile Apps, Startups, Financial APIs, Mortgages, Multi-tenant Architecture, OAuth, Dashboards, Scalable Architecture, Problem Solving, Orchestration, Data, Convex, Billing, MVP Design, AI Automation, Front-end Architecture, Software Design, API Design, CMS, WCAG 2, Web Content Accessibility Guidelines (WCAG), Cloud, Engineering Management, System Architecture, API Connectors, Identity & Access Management (IAM), Performance Optimization, RESTful Web Services, SEO Tools, ElevenLabs Solutions, Speech-to-Text (STT), Machine Learning Operations (MLOps), Event Streaming, Vector Databases, Data Modeling, Multi-tenant SaaS, Dashboard Development, Data Aggregation, AI Tools, AI Model Training, RTL, GeoJSON, Real Estate, Vite, Product Mindset, Ruby on Rails 8, Monday.com, Web App Development, Healthtech, Medical Software, Software Engineering, Generative Artificial Intelligence (GenAI), Mobile-first Design, QR Codes, Video Processing, Videos, Email Automation, 2D Image Processing, Image Processing, Monte Carlo Simulations, Application Security, IT Security, Payment APIs, Web Security, Systems Design, API Documentation, Application State Management, Interactive UI, Monitoring, Responsive UI, AI Governance, AI Testing, OOP Designs, Software Documentation, Package Design, Observability, Automations, Data Extraction, Inventory Management, Scripting, Manufacturing Resource Planning (MRP), Supply Chain Operations, Supply Chain, Webex, SDKs, Product Lifecycle Management (PLM), Analytics, Early-stage Startups, Apple Pay, Google Analytics 4 (GA4), Single Sign-on (SSO), Server-side Rendering (SSR), Apify SDK, FaunaDB, claw code, Embedding Models, Natural Language Processing (NLP), Recommendation Systems, Authorization, Query Optimization, ChatGPT API, Azure Blog Storage, Cloud Security, Microsoft Azure, Security, role based access control, UTM Parameters, Design Systems, Storybook, AI Architecture, Pixel Perfect, Dagster, DuckDB, Devin, Web Application Design, Development, Content Management Systems (CMS), Digital Marketing, Vibe Coding, Double-entry Bookkeeping, Bots, BAPI, Business Application Programming Interface, OData, SAP, SAP Open Data Protocol (OData), Open Source, Data Encryption, Third-party APIs, Browsers, Digital Rights Management (DRM), TV, Industrial Automation Communication Protocols, Data Governance, Microsoft Graph API, RESTFul APIs, RESTful Microservices, Zustand, Portals, Web Administration, System Integration, Maps, Landing Pages, Web Marketing, Affiliate Marketing, Performance, Privacy, ETL Pipelines, Fine-tuning, Generative Pre-trained Transformers (GPT), Research, ETL for AI, Containers, Simulation Orchestration, HPCC Systems, Simulation Engines, Simulations, AI-generated Code, Code Review, UI Development, Security Architecture, Bug Fixes, Monorepos, Video Editing, Cloudflare Durable Objects, Production Engineering, Business Process Automation, Make.com, SQLModel, AI Chatbots, Chatbots, Team Leadership & Supervision, Finance, OpenAI SDK, AWS Auto Scaling, Core Web Vitals, A/B Testing, AI Engineering, Amazon DocumentDB, Image Manipulation, Fractional CTO, Legal Technology (Legaltech), Software as a Service (SaaS), System Optimization, Product Ownership, Optimization, Internet of Things (IoT), Reporting, Reports, AI Model Integration, Web Applications, Design, Travel, Data Integrity, Mobile App Security, Shopify Customizations, Pub/Sub, WebSockets, Anthropic, Document Parsing, Gmail, CSV, Pipelines, User Roles, Product Owner, Auditing, Audits, Data Architecture, ELT, Google BigQuery, LLM Agents, Reliability, Microsoft Dataverse, Infrastructure as Code (IaC), Online Bidding, AI Development, Streaming, AI Compliance, AI Security, Enterprise Systems, AI Workflow, ChatGPT Prompts, Reviews, Go-to-market (GTM) Strategy, Product Roadmaps, Code Auditing, Knowledge Graphs, Azure Blob Storage, Chrome Extensions, Microsoft 365, Amazon Bedrock, High Availability (HA), SQL Server, Amazon RDS, System Design, AI Safety, Chromium, Digital Banking, Microfinancing, Pgvector, Search Engines, Vector Search, CRM developer, UI Components, Single-page Applications (SPAs), BigCommerce Stencil Design, Gemini, Trading, Mobile UX, OpenAI, OpenTelemetry, Prometheus
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