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Kazusa Tsubota

@kazusatsubota1

Full-stack AI engineer building products with Next.js, Python, and LLM agents. Skilled in RAG, AWS, and production monitoring.

Japan

Message

I'm a full-stack engineer with 7+ years of experience building products across retail SaaS, Web3, and AI. At ScalyX.ai, I develop a retail management platform with Next.js, Python/FastAPI, and PostgreSQL, and build AI agents that combine RAG, semantic search, and tool calling to help users find information and complete workflows. I also work with LangChain, LangGraph, A2UI, and Whisper to create interactive and voice-enabled agent experiences.

My experience spans frontend architecture, BFF and API design, cloud infrastructure, and production observability. At AllWeb3, I led the technical direction of a Next.js and React frontend, shaping its architecture, project structure, and reusable component system. I have operated services on AWS and Kubernetes, including a migration for a platform serving 30+ tenants that reduced average monthly infrastructure costs by approximately 17%. I also build cross-platform mobile apps with React Native and Expo. I enjoy owning product features end to end and working closely with product and design teams.

Experience

Work history, roles, and key accomplishments

Current

Mobile / Web Engineer

Current

Madoromi, Inc

Aug 2026 - Present (3 months)

Developed a cross-platform iOS and Android application with React Native and Expo, including onboarding and API integration. Built the user-facing website with Next.js, including authentication and subscription checkout.

React Native Expo Next.js Clerk Stripe Deep Links

Current

Full-Stack / AI Application Engineer

Current

ScalyX.ai

Jan 2024 - Present (2 years 10 months)

Built retail management features using Next.js, Python/FastAPI, and PostgreSQL. Developed RAG agents with LangChain/LangGraph, semantic search, and tool calling; added A2UI responses and Whisper speech-to-text. Set up Prometheus, Grafana, OpenTelemetry, Jaeger, and CloudWatch, cutting investigation time 40%. Migrated 30+ tenants to shared AWS EKS, reducing monthly infrastructure costs ~17%.

Infrastructure / Full-Stack Engineer

AllWeb3

Jan 2022 - Oct 2023 (1 year 9 months)

Led technical direction for a Web3 marketing platform, designing frontend architecture and a BFF layer. Consolidated backend services into a NestJS monorepo, reducing infrastructure costs.

Next.js React TypeScript NestJS PostgreSQL BFF TurboRepo AWS Lambda EventBridge OpenAPI

Full-Stack Engineer

StoreHub

Dec 2018 - Dec 2021 (3 years)

Developed inventory management features for a cloud POS and retail SaaS platform, building React and Next.js interfaces and Node.js REST APIs. Implemented employee management features and inventory import tools.

React Next.js NodeJS REST APIs PostgreSQL CSV Excel SQL