David Kalinowski - Senior Software Engineer

Q: Where is David based?

David is based in Sejny, Poland .

Q: What languages does David speak?

David speaks the following languages: English (Advanced), Polish (Intermediate) .

Q: How many years of experience does David have?

David has at least 10 years of experience. During this time, David has worked in at least 2 different roles and for 3 different companies . The average length of individual experience is 3 years and 3 months . Note that David may not have shared all experience and actually has more experience.

Q: What is David's latest experience?

David's most recent position is Senior Software Engineer at Brainreader A/S .

Q: What companies has David worked for in recent years?

In recent years, David has worked for Brainreader A/S and Accedia .

Q: Which industries is David most experienced in?

David is most experienced in industries like Information Technology (IT) and Healthcare .

Q: Which business areas is David most experienced in?

David is most experienced in business areas like Information Technology (IT) and Product Development .

Q: Which industries has David worked in recently?

David has recently worked in industries like Healthcare and Information Technology (IT) .

Q: Which business areas has David worked in recently?

David has recently worked in business areas like Information Technology (IT) and Product Development .

Recommended expert

Sejny, Poland

Experience

Oct 2022 - Present

3 years 6 months

Senior Software Engineer

Brainreader A/S

Built secure backend services in Nest.js and Python (FastAPI) to process sensitive healthcare data, ensuring HIPAA-compliant storage and fast API performance.
Developed patient dashboards and mobile wellness features using React, Next.js, and React Native, optimizing cross-platform usability for clinical and user-facing apps.
Built a streaming chat UI with MUI in React/Next.js and React Native Paper while cutting UI build time 40% and improving task completion 20% across clinician workflows.
Implemented secure JWT and OAuth2 authentication flows with RBAC for role-based access across dashboards, APIs, and mobile platforms.
Shipped an LLM-powered symptom checker (OpenAI + LangChain, RAG on clinical notes) that reduced triage time 30% and increased self-serve resolutions significantly.
Designed REST and GraphQL APIs with strict validation and clear versioning, enabling smooth frontend integration and reliable data flow between systems.
Used TypeORM and SQLAlchemy to model patient records, health events, and permissions, supporting migrations and relational integrity in PostgreSQL.
Implemented automated testing across backend (Pytest, Jest) and frontend (React Testing Library), covering unit, integration, and E2E scenarios, improving code reliability and reducing production bugs.
Optimized prompts, caching, and batching; lowered monthly token spend ~25% while keeping medical guidance accuracy within policy thresholds.
Reduced backend response time by 40% through async job queues, caching with Redis, and refactoring API bottlenecks in high-traffic modules.
Architected schemas in PostgreSQL and MongoDB and Elasticsearch for storing structured and unstructured medical data, including lab results, appointments, and logs.
Deployed services on AWS and Azure using Docker and Kubernetes, S3, Lambda, and Blob Storage, ensuring scalability, data privacy, and high availability.
Set up GitHub Actions and Terraform pipelines to automate tests, builds, and secure deployments across dev, staging, and production.
Led cross-functional sprints with product, design, and data teams, mentored juniors, and translated technical goals into user-centered outcomes in fast-moving environments.

Mar 2020 - Aug 2022

2 years 6 months

Senior Software Engineer

Accedia

Built high-throughput backend pipelines by migrating legacy NodeJS to Django, and Celery to power task queues and annotation flows across massive, distributed datasets.
Created custom React hooks to handle forms, API calls, and UI logic, making the code cleaner and helping the team build features faster.
Integrated third-party SSO providers Google and Auth0 to enable seamless login and centralized access control across teams and datasets.
Built AI-powered pipelines with LangChain and LangGraph to automate data labeling workflows, combining human-in-the-loop checks, confidence scoring, and scalable orchestration and cut review time by 50%.
Structured flexible data schemas using Prisma, SQLModel and Elasticsearch to handle millions of records, including raw inputs, metadata, and annotation revisions.
Used React Query and visualized AG-Grid on large datasets to handle data fetching with smart caching, background updates, and batching, keeping the UI fast and responsive during heavy labeling tasks.
Deployed RAG services with AWS Lambda, S3, and RDS; reduced inference cost per user by ~22% and kept latency under 700 ms during peak time.
Built CI/CD pipelines with automated testing and deployment using GitHub Actions and Docker, enabling fast, reliable releases with easy rollback across staging and production.
Worked closely with ML engineers, data ops, and product leads to align infrastructure with evolving annotation workflows and model training cycles.

Feb 2016 - Dec 2019

3 years 11 months

Junior Software Engineer

Synerise

Built small web apps using React (Hooks, React Router) and Node.js (Express).
Worked with PostgreSQL and SQLite for databases and used socket.io to add real-time features like chat and notifications.
Focused on clean and responsive UIs using HTML5, CSS3, and Material UI components.
Worked with version control using Git and GitHub, tested APIs with Postman, and collaborated through pull requests.
Communicated effectively, asked the right questions, took feedback well, and supported team collaboration in agile environments under senior developers.

Industries Experience

See where this freelancer has spent most of their professional time. Longer bars indicate deeper hands-on experience, while shorter ones reflect targeted or project-based work.

Experienced in Information Technology (6.5 years) and Healthcare (3.5 years).

Information Technology

Healthcare

Business Areas Experience

The graph below provides a cumulative view of the freelancer's experience across multiple business areas, calculated from completed and active engagements. It highlights the areas where the freelancer has most frequently contributed to planning, execution, and delivery of business outcomes.

Experienced in Information Technology (9.5 years) and Product Development (7.5 years).

Information Technology

Product Development

Summary

Senior Full Stack Web Developer with 9+ years of experience delivering high-impact web and mobile platforms across healthcare, AI, and SaaS industries. Specialized in React, Next.js, and Node.js with strong backend expertise in Python, FastAPI, and scalable infrastructure using AWS and Azure. Proven success in building real-time systems, clean and testable APIs, and leading cross-functional teams with a focus on performance, CI/CD automation, and developer experience.

Skills

Programming Languages

Node.js
Java
Python
Javascript
Typescript
Html5
Css
Json
Yaml
Kotlin

Frameworks & Libraries

Fastapi
Django
Flask
Pandas
Numpy
Express
Nest
Next
React
React Native
Redux
Vue
Angular
Vite
Webpack
Tailwindcss
Mui
D3.js
Antd
Ag-grid

Database & Orm

Postgresql
Mysql
Mongodb
Dynamodb
Django Orm
Sqlalchemy
Prisma
Typeorm
Sequelize
Mongoose
Redis
Realm
Clickhouse
Integresql

Architecture

Microservices
Microfrontends
Software Design Patterns
Oop (Object-oriented Programming)
Solid Principles
Dry
Tdd
Restful Api
Graphql
Swagger
Storybook
Webhooks

Cloud & Devops

Aws (Ec2, Ecs, Eks, Cognito, Lambda, Api Gateway, S3, Rds, Sns, Sqs)
Azure
Gcp
Ci/cd
Docker
Kubernetes
Jenkins
Github Actions
Aws Cdk
Cloudformation
Terraform
Grafana

Others

Kafka
Rabbitmq
Aws Sns/sqs
Grpc
Unit Testing
E2e Testing
Pytest
Jest
Mocha
Localstack
Playwright
Cypress
Postman
Agile/scrum
Jira
Slack
Mentoring
Pair Programming
Code Review
Troubleshooting
Problem Solving
Collaboration & Communication
Llm & Genai
Pinecone
Weaviate

Languages

English

Advanced

Polish

Intermediate

Education

Oct 2012 - Feb 2016

Bialystok University of Technology

Bachelor’s degree · Białystok, Poland

Profile

Created

October 2025

Last Update

December 2025

Need a freelancer? Find your match in seconds.

Try FRATCH GPT

Frequently asked questions

Do you have questions? Here you can find further information.

Where is David based?

David is based in Sejny, Poland.

What languages does David speak?

David speaks the following languages: English (Advanced), Polish (Intermediate).

How many years of experience does David have?

David has at least 10 years of experience. During this time, David has worked in at least 2 different roles and for 3 different companies. The average length of individual experience is 3 years and 3 months. Note that David may not have shared all experience and actually has more experience.

What roles would David be best suited for?

Based on recent experience, David would be well-suited for roles such as: Senior Software Engineer, Junior Software Engineer.

What is David's latest experience?

David's most recent position is Senior Software Engineer at Brainreader A/S.

What companies has David worked for in recent years?

In recent years, David has worked for Brainreader A/S and Accedia.

Which industries is David most experienced in?

David is most experienced in industries like Information Technology (IT) and Healthcare.

Which business areas is David most experienced in?

David is most experienced in business areas like Information Technology (IT) and Product Development.

Which industries has David worked in recently?

David has recently worked in industries like Healthcare and Information Technology (IT).

Which business areas has David worked in recently?

David has recently worked in business areas like Information Technology (IT) and Product Development.

What is David's education?

David holds a Bachelor from Bialystok University of Technology.

What is the availability of David?

David is immediately available full-time for suitable projects.

What is the rate of David?

David's rate depends on the specific project requirements. Please use the Meet button on the profile to schedule a meeting and discuss the details.