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Saroz MitraSaroz MitraFull-Stack Engineer
Open to contracts & startup collaborations

Building AI systems from infrastructure to interface.

RAG Pipelines · Python · Cloud Infrastructure · Next.js

I design and build AI-enabled applications end to end - from retrieval architecture and LLM integration to cloud infrastructure and frontend delivery. Currently building a production RAG system for a healthcare AI platform with hybrid search, multi-layer safety guardrails, observability, and real-time streaming.

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Technical Expertise

Working daily across Python, Next.js, GCP, and Terraform - complete systems from infrastructure to interface.

AI Engineering

Production RAG pipelines with hybrid retrieval, LangChain orchestration, multi-layer guardrails, and observability.

RAGLangChainLLMsvLLMChromaDBLangfuse

Backend

Python-first backend with FastAPI, async pipelines, caching strategies, and PostgreSQL.

PythonFastAPIPostgreSQLRedisWebSocket

Frontend

Component-driven UI with Next.js, React, and TypeScript. Design systems, state, and performance.

Next.jsReactTypeScriptZustandStorybook

Cloud & Infra

Infrastructure as code with Terraform on GCP. Docker, CI/CD, and environment reproducibility.

TerraformGCPDockerFirebaseCI/CD

Selected Work

Spanning healthcare AI, global e-commerce, and recruitment platforms.

Client
ARGC · Blue Door Fertility
Stack
PythonFastAPIChromaDBvLLMOllamaLangfuseRedisPostgreSQLDocker

ARGC RAG Pipeline

Healthcare AI Retrieval System

Production RAG system for a patient-facing IVF clinic AI assistant. Multi-stage pipeline with hybrid retrieval, multi-layer safety guardrails, and full observability.

  • -Designed hybrid retrieval - BM25 + vector search with Reciprocal Rank Fusion, intent and treatment-stage boosting
  • -Built multi-layer guardrails: input safety, output validation, dialog monitoring, medical safety, faithfulness checking
  • -Introduced ChromaDB and built the ingestion pipeline from Notion CSV exports
  • -Designed two-tier response caching (L1 in-memory + L2 Redis) - reduced repeat query latency from ~5s to under 10ms
  • -Integrated Langfuse for full request tracing with per-stage spans and confidence scoring
  • -Implemented circuit breaker pattern on guardrails for resilience
  • -Built comprehensive test suite across unit, integration, and API layers
Outcome

Production system serving real patients at an IVF clinic. Evaluation test cases across multiple datasets for regression testing.

Client
ARGC · Blue Door Fertility
Stack
Next.js 14TypeScriptReactZustandWebRTCWebSocketFirebasePythonTerraformGCP

ASHA - AI Fertility Assistant

AI Conversational Avatar Platform

Next.js application with real-time WebRTC video avatar streaming, voice interaction via Deepgram, WebSocket AI responses, and Terraform-managed GCP infrastructure.

  • -Built the entire frontend - custom React hooks organised by domain (auth, avatar, chat, voice, WebSocket, session), component library, and Zustand state management
  • -Implemented dual interaction modes: text chat with streaming responses, and video mode with real-time voice capture, transcription, and avatar lip-sync
  • -Built admin dashboard - conversation viewer, search/filter, PDF transcript export, analytics
  • -Wrote Python Cloud Functions for analytics logging and embryology access control
  • -Designed Terraform infrastructure: VPC, Cloud SQL, Cloud Functions, Secret Manager, IAM - across dev/staging/prod
  • -Built unit and end-to-end test coverage with Jest and Cypress
Outcome

Live production app serving IVF patients. Dual interaction modes (chat + video avatar). Full admin visibility into conversations. Infrastructure reproducible across three environments via Terraform.

Client
PVH · Calvin Klein / Tommy Hilfiger
Stack
Next.jsReactTypeScriptRedux ToolkitStorybookNode.jsAdyenCypress

PVH Unified Checkout

Enterprise E-Commerce Platform

Unified checkout experience for Calvin Klein and Tommy Hilfiger across 25 countries, replacing fragmented per-country implementations.

  • -Consolidated fragmented per-country checkout codebases into a single unified platform serving both brands across 25 countries
  • -Engineered the component design system using Storybook for UI consistency across both brands and all country configurations
  • -Integrated Adyen payment gateway - credit/debit, PayPal, 3DS1/3DS2 authentication flows
  • -Implemented multi-lingual support, dynamic address fields per country, promotions management, and session handling
  • -Optimised frontend performance across server-side rendered pages and checkout flows
  • -Built reusable React component library shared across multiple development teams
  • -Built comprehensive test coverage - unit (Jest), integration (React Testing Library), E2E (Cypress)
Outcome

Unified checkout live across 25 countries for two major fashion brands. Single maintainable codebase replacing fragmented per-country implementations.

Professional Journey

18 years across healthcare AI, global e-commerce, fintech, and biotech.

Sep 2024 - Present
Full-Stack Engineer
ARGC / Blue Door Fertility
London, UK · Contract

Building two connected production systems for a healthcare AI platform: a Python RAG pipeline and a Next.js conversational avatar interface, with supporting GCP infrastructure.

PythonFastAPIChromaDBLangfuseNext.jsWebRTCTerraformGCP
Apr 2023 - Sep 2024
Senior Frontend Developer
Experts Circle
London, UK · Contract

Delivered key features for a recruitment platform including job aggregation, candidate matching, and notification systems. Built reusable component library and mentored junior developers.

ReactTypeScriptAWS LambdaDynamoDBStorybookTerraform
Sep 2019 - Mar 2023
Senior Frontend Developer
Wunderman Thompson Commerce (VML)
Watford, UK · Contract

Unified checkout for Calvin Klein and Tommy Hilfiger across 25 countries. Integrated Adyen payments, multi-lingual support, and SSR-optimised performance.

ReactRedux ToolkitNext.jsTypeScriptAdyenStorybook
Mar 2019 - Sep 2019
Software Engineer
Sartorius
Royston, UK · Contract

Built the frontend for a clone selection application used in biotech research. Integrated GraphQL APIs with React and Redux Toolkit, and worked with Python services on Azure infrastructure.

ReactRedux ToolkitGraphQLPythonMongoDBAzure
Sep 2018 - Dec 2018
UI Developer
Barclays
Northampton, UK · Contract

Developed single-page applications for Barclaycard financial services using React and Redux. Focused on responsive design and accessibility compliance for banking products.

ReactRedux ToolkitJavaScript
May 2015 - Jul 2018
Senior Frontend Developer
Flixmedia Limited
London, UK · Permanent

Built e-commerce web solutions for major retail brands. Introduced Vue.js for an internal dashboard application, led frontend architecture decisions, and mentored junior developers across multiple frameworks.

ReactVue.jsAngularRedux ToolkitTypeScript
Dec 2010 - May 2015
Frontend Developer
BNP Paribas (Cardif Pinnacle Insurance)
London, UK · Permanent

Built UI/UX for online insurance and financial products. Ensured W3C compliance and accessibility standards, implemented responsive designs, and integrated with backend APIs for policy management systems.

HTML5CSS3JavaScriptjQuery

What colleagues say

From product leaders, engineers, and managers across healthcare AI and enterprise e-commerce.

“I worked with Saroz on an AI customer support avatar product at Blue Door Fertility. He is an intelligent and capable engineer with a great can-do attitude. A real pleasure to work with - I hope I can again in future.”
Gideon SummerfieldGideon SummerfieldProduct Leader · Sky, BBC, Hive, Start-ups
“Saroz always goes above and beyond to find the best technical solutions to issues and new feature requests. Thanks to his exceptional attention to detail, he produces top quality code. He is great at collaborating with other team members in all phases of the project, he is flexible and always willing to help his colleagues.”
Marianna FalchiMarianna FalchiBusiness Analyst · VML
“Saroz is very professional and talented developer. He is curious and extremely knowledgeable. He has great technical skills, and always seeks to further them. Saroz is ready to help the team members to achieve their goals. Hard working, dedicated, adaptable and very focused.”
Katarzyna Hrycek-RobinsonKatarzyna Hrycek-RobinsonSenior Test Engineer · VML
“It was a true nice experience to work with Saroz. His sharp eye and craftsmanship has helped a lot to achieve the product goals. He works thoroughly and has a high quality standard for coding. He's a real team player and a nice guy.”
Michiel KramerMichiel KramerSenior Lead Product Owner · PVH / Calvin Klein / Tommy Hilfiger
“Saroz was a core team member in a development team that built and rebuilt ecomm checkout of two major fashion brands, TH and CK. He has demonstrated a very high standard and quality of work throughout the project.”
Justyna LatkoJustyna LatkoSenior Product Manager · PVH Europe B.V.
“Saroz is a solid front-end developer that worked in a product team on one of our major accounts. He is very experienced in React technologies, communicates well and conducts himself in a professional manner. I would happily use his services again and recommend him.”
Nat GaleNat GaleHead of Product Engineering EMEA · Magentus
“Saroz and I have worked together in a scrum team to improve the Tommy Hilfiger & Calvin Klein checkouts. It has been a pleasure working with Saroz from start to end. He is a dedicated, hard working developer who delivers high quality code. It is easy to communicate with Saroz, always willing to help out. Thanks Saroz!”
Janna van AalderenJanna van AalderenInterim Product Owner / Project Manager · Your Guiding Light
Contact

Let’s work together.

Open to contract roles in the UK where I can work across the stack - AI systems, backend services, cloud infrastructure, and the interfaces on top of them.

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