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Muhammad Tahir Hassan Khan · Backend Software Engineer

Backend Software Engineer Building Reliable, Scalable Products

I design backend architecture, integrations, background-job systems, and AI features for SaaS products, most recently a multi-tenant healthcare platform used by hospital systems.

Production work across healthcare SaaS, online education, and e-commerce with Node.js, Python/FastAPI, PostgreSQL, MongoDB, Redis, FHIR/HL7, Twilio, and LLM services.

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  • Nearly 3 Years in Production
  • Multi-Tenant Healthcare SaaS
  • EHR / FHIR Integrations
  • Background Job Systems
  • LLM Features in Production
  • End-to-End Subsystem Ownership

Selected case studies

Problems solved in production

How I approach real backend problems: context, decisions, and trade-offs.

What I do

Backend Engineering Beyond CRUD APIs

My work sits where backend systems get hard: data from many external sources, work that runs in the background, rules that must hold for every tenant, and AI features in a regulated product. I design these systems so the important rules are enforced in one place and failures don't reach the people using them.

  • Backend Development

    You need a backend that holds up in production. I build APIs for web and mobile apps with Node.js or Python/FastAPI, on PostgreSQL, MongoDB, and Redis.

  • Multi-Tenant SaaS Backends

    Serving several customers from one product? I scope every query, job, and cache key to the right tenant so data never leaks between them.

  • Healthcare & EHR Integrations

    FHIR/HL7 and EHR vendor APIs, normalized into one model so each new hospital or vendor doesn't mean rewriting your product.

  • Background Jobs & Messaging

    Scheduled and event-driven work on Bull/BullMQ and Redis, with SMS and voice over Twilio that respects consent and quiet hours.

  • AI Features in Production

    RAG chatbots, LLM triage, and document generation added to your product with guardrails, fallbacks, and per-customer rollout.

  • Existing Backend Improvement

    A backend that's hard to change or quietly wrong? Audits, root-cause fixes, tests that prove concurrency and money logic, and safe expand/contract migrations.

How I can help

Featured projects

Systems I've built

Work across a healthcare SaaS platform and a multi-country tutoring platform (both confidential), plus Sokkat, a UAE e-commerce mobile app.

Healthcare SaaS / Workflow Automation

Patient Journey Automation Engine

Problem
Pre-op instructions, consent collection, post-op check-ins, and outcome surveys were coordinated largely by hand, with no consistent way to reach the right patient at the right time.
What I built
A state-machine journey engine driven by appointment events, with consent and quiet hours evaluated once, centrally, as gates for every channel.
My role
Owned design and implementation, State-machine journey logic, Consent and quiet-hours gating, Handling reschedules, cancellations, readmissions, and out-of-order events
  • Node.js
  • Express
  • MongoDB
  • Bull / BullMQ
  • Redis
  • Twilio
Project details Read case study

Healthcare Interoperability

EHR Integration Layer

Problem
Each hospital ran a different EHR vendor with its own data formats, timezones, and event semantics, so nothing could be built once and reused safely across hospitals.
What I built
Per-vendor FHIR/HL7 adapters feeding a clinical event normalization layer, with explicit per-site timezone handling.
My role
Built and maintained the integration layer, Clinical event normalization, Per-site timezone handling, Vendor adapter design
  • Node.js
  • FHIR
  • HL7
  • EHR vendor APIs
  • MongoDB
Project details Read case study

SaaS Infrastructure

Multi-Tenant Data Access & Job Infrastructure

Problem
Bursts of EHR events and messaging campaigns from many hospitals had to be processed without cross-tenant leakage or duplicate sends.
What I built
Data-access patterns that scope every query, job payload, and cache key to a hospital, plus idempotent jobs on tenant-partitioned Redis queues.
My role
Designed multi-tenant data access patterns, Built background job infrastructure, Idempotent job design, Auth0 / JWT validation
  • Node.js
  • MongoDB / Mongoose
  • Redis
  • Bull / BullMQ
  • Auth0
  • JWT
Project details Read case study

AI / Healthcare

LLM Features in Clinical Workflows

Problem
AI chat and triage carried real patient-safety edge cases, such as an opted-out patient receiving an AI reply or a clinical note drafted without human review.
What I built
An isolated LLM service boundary with consent and tenant checks ahead of every call, defined fallbacks for a degraded service, and per-hospital enablement.
My role
Integrated RAG chat, triage, and note drafting, Consent and tenant checks before every LLM call, Fallback behavior for LLM outages, Voice AI agent integration
  • Node.js
  • LLM / RAG services
  • Twilio Voice
  • MongoDB
Project details Read case study

EdTech / SaaS / Full-stack

Multi-Country Online Tutoring Platform

Problem
A tutoring business running on prepaid hours needed reliable self-service booking, correct tutor pay, and trustworthy notifications, on code built for subscriptions whose tests hid real bugs.
What I built
A hardened booking engine, a credit-hours model, a single tutor-pay seam and finance hub, enumeration-safe public IDs, a notification centre with reply-by-link, and performance and cost fixes.
My role
Booking engine audit and hardening, Credit-hours domain model, Tutor pay seam and finance hub, Public-ID allocator and visibility rules
  • Python
  • FastAPI
  • SQLModel
  • Alembic
  • PostgreSQL
  • Redis
Project details Read case study

E-commerce / Mobile Backend

Sokkat

Problem
A UAE-based e-commerce store selling through Shopify needed a backend for its mobile app.
What I built
Node.js APIs consumed by the mobile app, integrated with the store's Shopify backend and backed by PostgreSQL.
My role
Backend engineer (2023–2024), Node.js API development for the mobile app, Shopify backend integration, PostgreSQL data layer
  • Node.js
  • PostgreSQL
  • Shopify
Project details
All projects

Technical expertise

The stack I work in

Backend
Node.js, Express, Python, FastAPI, SQLModel / SQLAlchemy, Bull / BullMQ
Databases
PostgreSQL, MongoDB / Mongoose, Redis, Alembic migrations
Auth & Multi-Tenancy
Auth0, JWT validation, Tenant-scoped data access, HMAC-signed tokens
Healthcare Interoperability
FHIR, HL7, EHR vendor APIs, Clinical event normalization
Integrations
Twilio SMS & Voice, Voice AI agents, Shopify, SMTP & push
AI / LLM
RAG chatbots, LLM triage, Clinical note generation
Frontend & Mobile
TypeScript, Next.js, React, SWR, Flutter
Testing
pytest, Mocha / Chai / Sinon, Vitest, Playwright, Testcontainers
Delivery
CI-gated deploys, Expand/contract migrations, Sentry

Experience

Professional experience

  1. Backend Software Engineer · Healthcare technology company (name under NDA)

    Nearly 3 years · Present

    • Progressed from backend feature engineer to owner of several core subsystems on a multi-tenant care-coordination platform
    • Owned the patient journey automation engine: state-machine-driven outreach based on appointments, consent, and quiet hours
    • Built and maintained the EHR integration layer, normalizing multi-vendor clinical events into a common FHIR-based model
    • Designed tenant-scoped data access across queries, background jobs, and cache keys
    • Built Bull/BullMQ + Redis job infrastructure for scheduled and event-driven patient outreach
    • Integrated LLM features (patient chat, triage, clinical note drafting) with consent checks and outage fallbacks
    • Contributed to the patient-reported outcomes analytics pipeline and campaign messaging systems

  2. Full-Stack Engineer · Multi-country online tutoring platform (confidential)

    [ADD DATES · X MONTHS]

    • Audited and hardened the self-service booking engine, adding Postgres-backed tests that prove its row locks work
    • Modelled the credit-hours booking domain so admin-granted hours became spendable
    • Centralised tutor pay into one server-side rate seam and built a unified finance hub
    • Designed enumeration-safe, org-scoped public IDs with per-recipient visibility
    • Audited 49 notification issues, closed a link-poisoning vulnerability, and built reply-by-link
    • Cut the slowest dashboard route from 11.0 s to 3.8 s and removed hosting-cost drivers

  3. Backend Engineer · Sokkat (UAE-based e-commerce)

    2023 — 2024

    • Built Node.js APIs powering the Sokkat mobile app
    • Integrated the app with the store's Shopify backend
    • Worked with PostgreSQL for the backend data layer

How I work

Engineering principles

  • Root cause, not symptom

    I trace a reported bug back to the shared code path every caller goes through and fix it there.

  • Make critical rules structural

    Tenancy, consent, and quiet hours are enforced at one layer, not re-checked in every feature.

  • Decouple slow work

    Messaging and integrations run as idempotent background jobs, so failures retry safely and never block a workflow.

  • Roll out in phases

    Feature flags and per-tenant enablement, so changes can be rolled back without a redeploy.

  • Prove the safety claims

    Tests run on the real database engine, and mutation tests show a lock or guard actually prevents the failure.

  • Keep humans in the loop

    AI goes where it's safe. Where patient safety is involved, a person reviews the output.

Need a backend engineer who owns it end to end?

From architecture to production support, I take features from requirements to running software.

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Have a Backend Problem to Solve?

If you're building a SaaS product, improving an existing backend, integrating third-party services, or dealing with performance issues, let's discuss the problem.