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Muhammad Zaeem Khan

Muhammad Zaeem Khan

Senior Backend Engineer | SaaS & Mobile | Agentic Engineering

Specialties: Multi-Tenant SaaS on Postgres & Supabase, Enterprise C# / .NET Backends, HIPAA Healthcare Platforms, Shipping with Claude Code & Codex, Restaurant POS & Payment Integrations, White-Label E-Commerce for US Retailers, Stripe Connect Payments & Payouts, Multi-Tenant ASP.NET Core with CQRS, Trader Apps for iOS & Android, Flutter Apps Shipped to Both Stores, AI Chrome Extensions & RAG Chat Agents, Error Monitoring & Tracing with Sentry, Legacy Data Migration Wizards, Supplier Dropship & Order Automation, Uber Eats, Clover & Moneris Integrations, ML Kit Pose Detection on Android, Real-Time GPS Tracking with Socket.IO, Stock Signal Dashboards in React 19, Xamarin Apps with Twilio VoIP, WinForms Desktop Systems & T-SQL, Web Scraping & Price Tracking Tools.

Now faster with AI, and every change is still tested and reviewed.

Available for new projects

Years Experience
16+
Projects Shipped
55+
Mobile Apps Shipped
35+
Remote Since
2011

About Me

Currently building: Multi-Tenant SaaS & HIPAA Healthcare Platforms

I'm a senior backend engineer with 16+ years of shipping production software, end to end. I build SaaS platforms, mobile apps and enterprise backends for healthcare, fintech, e-commerce, restaurant POS, and beauty & wellness businesses.

Lately I've been hardening the database security and CI guardrails of a multi-tenant salon & spa SaaS, and rolling out error monitoring with patient-data scrubbing on a HIPAA healthcare portal. I build with Claude Code and Codex, and every change still clears tests and code review before it ships.

Agentic Engineering

Claude Code, Codex, OpenAI APIs, test-gated delivery

Full Stack

.NET, Node.js, PHP, React, Postgres, Supabase

55+ Projects Shipped

Healthcare, fintech, POS, e-commerce

Mobile

Android, iOS, Flutter, KMP, React Native

Companies I've Built For

SaaS platforms, healthcare, US grocery retail, restaurant POS, fintech and enterprise. Remote delivery to US / UK / EU teams since 2011.

NeonO

Multi-tenant salon & spa platform

Beauty & Wellness SaaS

Pt Pal

HIPAA therapy app & clinician portal

Healthcare

Pepsi Cola

Enterprise MIS, 300+ employees

Manufacturing

GrocerKey / Point Pickup

10+ US grocery retailers

E-Commerce

Black Tower Investments Ltd.

Trader companion apps

Fintech

Dialoct

US legal platform

Legal Tech

ABS POS / WinRest

20+ year-old POS codebase

Restaurant POS

How I Work

I'm the engineer responsible for your project. Claude Code is my daily driver, Codex double-checks its work, and nothing reaches your users until the tests pass and I've reviewed it. Pick a phase to see what happens there.

Phase 1 of 16

Discover

Should we build this, and which way?

Research

Before building anything, I check what already exists and what has changed recently, so you don't pay for something you could reuse.

Show the 8 detailed checks
  1. 1. Current signal: what developers and users say on Reddit, X, YouTube, Hacker News and GitHub in the last 30 days, not stale assumptions.
  2. 2. Preflight gate: research aborts before the first search if its sources are stale or its preconditions fail.
  3. 3. Reuse before build: existing libraries, tools and patterns are searched before any custom code is proposed.
  4. 4. Honest coverage: every source is reported as searched, skipped or failed. No silent skipping.
  5. 5. Cited findings: each claim traces to its source, and anything that drives a decision needs two independent sources.
  6. 6. Competitor tiers: rivals sorted into direct, adjacent and aspirational, then scored and pruned before any benchmarking.
  7. 7. Clear comparison: findings checked against your notes and labelled match, conflict, missing or stale.
  8. 8. Read-only boundary: research never touches live systems, keeps keys off public routes, and stops if a data format changes.

Explore Options

When the right approach isn't obvious, I build a quick throwaway version for you to try, so we decide on something real instead of guessing.

Show the 7 detailed checks
  1. 1. Throwaway prototype: built on a disposable branch when the wrong answer would be expensive to unwind.
  2. 2. Honest fidelity: behaviour questions get a working flow you can click; look-and-feel questions get real finish.
  3. 3. You settle it: your reaction to the prototype decides, not the agent's opinion of its own work.
  4. 4. Decision log: each outcome is written down so later work builds on it without reopening it.
  5. 5. Ideas across axes: options generated along distinct dimensions, and every rejected one keeps its reason.
  6. 6. Role panel: product, architecture, development and QA each respond to the same problem.
  7. 7. Tensions named: conflicting views are shown side by side, never averaged into a vague compromise.

Rule: no prototype runs unattended; if nobody can experience it, it waits.

Decide Direction

You get one clear recommendation based on your project, and for big decisions a second AI (Codex) challenges it before we commit.

Show the 8 detailed checks
  1. 1. Graded verdict: a decisive call grounded in your project, not a neutral pros-and-cons list.
  2. 2. Earned, not assumed: no verdict is given until there is enough project context to justify one.
  3. 3. Provenance: every supporting claim is tagged by where it came from: your code, your docs, or outside sources.
  4. 4. Own view first: a position is written down before any second opinion, so it cannot be anchored.
  5. 5. Independent advisors: four fresh reviewers receive only the question, never the prior discussion.
  6. 6. Codex critique: for high-stakes decisions, Codex reviews the draft decision as an outside model.
  7. 7. Consent first: nothing is sent out for external review without your explicit agreement.
  8. 8. No silent gaps: if the outside review cannot run, it is reported as missing, never quietly skipped.

Projects

Selected work from 55+ shipped projects

NeonO β€” All-in-One Salon & Spa Business Platform

NeonO β€” All-in-One Salon & Spa Business Platform

Multi-tenant SaaS that runs salons, barbershops and spas on one platform: online booking, staff scheduling, POS and payments, client CRM, marketing campaigns, reviews, an online store with supplier dropshipping, and an AI voice receptionist.

Web SaaS (React + Supabase)

React TypeScript Supabase PostgreSQL Deno Edge Functions +5
Pt Pal β€” Clinician Portal & Outcomes Dashboards

Pt Pal β€” Clinician Portal & Outcomes Dashboards

Clinician and organization portal behind the Pt Pal therapy app. Therapists, managers and org admins track patient adherence and outcomes, and the portal serves the mobile API, HL7 feeds, and scheduled survey and report jobs.

Web (PHP 8.3 + MariaDB)

PHP 8.3 MariaDB Power BI SQL Server Sentry +2
GrocerKey β€” White-Label Web Storefronts

GrocerKey β€” White-Label Web Storefronts

Enterprise white-label SaaS platform powering grocery storefronts for national retailers including Fareway, Kowalski's, and Stew Leonard's β€” with SSO authentication, Stripe payments, and LaunchDarkly feature flags for phased rollouts.

Web (TypeScript + Aurelia + React)

TypeScript Aurelia React Node.js Express +5
GrocerKey β€” Customer Web API

GrocerKey β€” Customer Web API

Customer-facing REST API powering GrocerKey's multi-retailer grocery storefronts β€” handling product catalog, search, pricing, promotions, cart/checkout, order tracking, and loyalty integration for millions of shoppers.

Backend (C# .NET)

C# .NET ASP.NET Core SQL Server Entity Framework +3
WinRest POS β€” Restaurant & Hospitality

WinRest POS β€” Restaurant & Hospitality

Enterprise-grade point-of-sale solution for the hospitality sector with secure real-time transactions.

POS Platform

C# .NET Firebird DB OAuth 2.0 Uber Eats API +4
Primary Sales Data Management System

Primary Sales Data Management System

Desktop enterprise application for managing primary sales data flows, accounting, reporting, and operational accuracy.

Desktop (C# .NET)

C# Windows Forms .NET SQL Server Azure

Pyriolo β€” Payment Gateway Integration

Integrated Heartland payment gateway into pizza delivery service websites including Marco's Pizza, Greek's Pizzeria, and Aver's Pizza. Enabled secure online payment processing for restaurant chains.

Backend (C# .NET)

C# .NET Heartland SDK SQL Server Payment Gateway +1
GrocerKey β€” E-Commerce Backend Services

GrocerKey β€” E-Commerce Backend Services

Enterprise-scale microservices backend processing millions of grocery transactions β€” CQRS architecture with RabbitMQ event queues, ElasticSearch real-time indexing, Redis caching, and multi-tenant support across 10+ retailer configurations.

Backend (C# .NET + Microservices)

C# .NET ASP.NET Core SQL Server Entity Framework +7
GrocerKey β€” Store & Operations API

GrocerKey β€” Store & Operations API

Store-facing operations API and background processing layer for GrocerKey β€” handling order fulfillment, inventory sync, picker integration, event logging, and scheduled data refresh across all retailer locations.

Backend (C# .NET)

C# .NET ASP.NET Core SQL Server RabbitMQ +3

Personal Projects & Side Work

Independent builds, not client or employer work. Chrome extensions, PWAs, automation tools I built in my own time to solve my own problems or explore new stacks via AI-assisted workflows.

Availability & Timezone Overlap

Remote with global clients since 2011. 40+ hours/week. Working hours 9 AM – 11 PM PKT (UTC+5), 14-hour daily window.

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UK / EU Central / Middle East

Strong

GMT, CET, Dubai (UTC+4)

Full 8-hour workday

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US East Coast

Strong

EST / EDT

5-hour morning overlap (9am–2pm their time)

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US Central

Strong

CST / CDT

4-hour morning overlap (9am–1pm their time)

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US Mountain / West Coast

Async

MST / PST / PDT

1-3 hour morning overlap, async-friendly

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Singapore / China

Strong

SGT (UTC+8)

5-hour afternoon overlap

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Australia East

Async

AEDT (UTC+11)

2-hour afternoon overlap

πŸ“ Based in Multan, Pakistan β€” Remote-only, no relocation

Client Reviews

What clients say after working with me

"Great experience working. Very professional, delivered tasks on time, and communicated clearly throughout the project. Highly recommended."

Database Expert β€” MongoDB + Flutter Sync & Local Storage

152 hours via Upwork
"Always delivers excellent results. On time and on budget. We only trust our development projects to Zaeem!"

WinRest Integration to Moneris GO Pinpad

46 hours via Upwork
Committed to Quality Reliable

Speaking & Seminars

Guest speaker at 5 universities, sharing real-world engineering experience, career paths and how the tech industry works

University of Southern Punjab, Multan

usp.edu.pk

Tech Industry Career Counselling β€” Jinnah Auditorium. Topics: Future of Tech Careers, AI & Cybersecurity, Career Roadmaps, Skills Industry is Looking For.

May 2025 USP Dept. of CS & IT Γ— Atrule Technologies

Experience

16+ years, from trainee to technical lead, with remote freelance work for US, UK and EU clients alongside full-time roles since 2011

Senior Backend Engineer (Freelance)

2023 – Present

Freelance / Upwork

Building AI-powered products, SaaS platforms, mobile apps, and enterprise backends for international clients. Flutter, React, .NET, NestJS, LLM integration.

Full Stack Developer

2022 – 2023

GrocerKey (Point Pickup Technologies)

E-commerce platform for grocery retailers. Built order modification flows (EBT/credit/gift/tips), user targeting for phased rollouts, and performance optimization under peak traffic.

Team Lead / Tech Lead

2020 – 2022

Atrule Technologies

Led a team building mobile apps (Flutter & Android), backend APIs (.NET), and nopCommerce e-commerce storefronts. Shipped 15+ apps to Play Store and App Store.

Senior Software Engineer

2017 – 2020

CLEVIATECH

Built WinRest POS integrations (Uber Eats, Clover, Moneris, Flyt), Dialoct lawyer-client platform (Xamarin + Twilio VoIP), and payment gateway integrations.

Senior Software Engineer

2014 – 2017

Pepsi Cola Bottler

Enterprise MIS for primary sales data management. Automated yearly closing processes, migrated business logic to stored procedures, and built HR salary management systems.

Junior Software Engineer

2012 – 2014

Green Fin Technologies

Desktop and web application development using C# .NET and SQL Server.

Education

BS Computer Science

2006 – 2010

COMSATS Institute of Information Technology

Islamabad, Pakistan

Currently available for freelance projects

Let's Work Together

I've spent 16 years making sure the hard parts get done right.

Bring me the problem that's been stuck. I'll ship the solution that isn't.

Prefer to see code first? GitHub @mzaeemkhan