• I’m a Senior Backend Engineer and full-stack software architect with over 7 years of coding experience across a broad stack. I design scalable systems, APIs, and user-centric frontends with a strong emphasis on reliability, maintainability, and performance.
• Core strength: building robust backends with .NET (ASP.NET Core, Web API, Razor Pages, Blazor), Java (Spring Boot), Node.js/NestJS, Next.js, and MERN/MEAN stacks. I thrive on solving complex problems with clean architecture, design patterns, and pragmatic engineering.
• I enjoy turning ideas into production-ready software, leading feature teams, and mentoring junior engineers. I’m passionate about software craftsmanship, automated testing, and DevOps practices that improve deployment velocity and system resilience.
• Tools & technologies span cloud-native architectures, microservices, event-driven design, REST/GraphQL APIs, CI/CD pipelines, containers, and telemetry/observability.

• Backend & API Design

  • .NET Framework and .NET Core / ASP.NET Core Web API
  • Razor Pages, Blazor (Server & WebAssembly)
  • Java Spring Boot (REST, microservices)
  • Node.js / NestJS (GraphQL & REST)
  • Next.js (Server Components, API Routes)
  • MERN/MEAN stack (MongoDB, Express, React/Angular/Vue, Node.js)

• Architecture & Patterns

  • Clean Architecture, SOLID, Domain-Driven Design (DDD)
  • Microservices, Monolith-to-Microservices strategies
  • Event-driven design, messaging (RabbitMQ, Kafka)
  • API design: REST, GraphQL, OpenAPI/Swagger

• Databases & Persistence

  • SQL Server, PostgreSQL, MySQL, MongoDB, Redis
  • ORM: Entity Framework Core, Dapper, Hibernate (Java)
  • Caching, data modeling, and performance optimization

• Frontend (Full-Stack Context)

  • Blazor (Server & WASM), Next.js, React-based frontends
  • Razor Pages, SPA patterns, responsive UI

• DevOps & Observability

  • CI/CD pipelines (GitHub Actions, Azure DevOps, Jenkins)
  • Docker/Kubernetes, cloud-native deployments
  • Logging, metrics, tracing (Serilog, OpenTelemetry, Prometheus, Grafana)

• Testing & Quality

  • Unit, integration, and end-to-end testing
  • Test-Driven Development (TDD) and Behavior-Driven Development (BDD)
  • Static code analysis, code quality gates

• Security & Compliance

  • OAuth2 / OpenID Connect, JWT
  • Secure API design, input validation, threat modeling

• Led end-to-end architecture and delivery of multiple large-scale backend systems using ASP.NET Core Web API, with clean architecture and domain-driven design.
• Built and scaled microservices with event-driven communication and robust data consistency strategies.
• Migrated legacy services to modern .NET Core and integrated modern frontend frameworks (Next.js, Blazor) to deliver cohesive UX.
• Designed and implemented secure RESTful endpoints, GraphQL schemas, and efficient data access layers.
• Implemented comprehensive testing strategies (unit, integration, contract testing) and automated CI/CD pipelines.
• Mentored engineers across frontend and backend teams, establishing best practices and coding standards.

• Backend: ASP.NET Core Web API, ASP.NET Razor Pages, Blazor, .NET Framework (legacy), Java Spring Boot, Node.js/NestJS
• Frontend / SSR: Next.js, Blazor, React, Razor Pages
• Databases: SQL Server, PostgreSQL, MySQL, MongoDB, Redis
• Message & Queues: RabbitMQ, Kafka
• Cloud & Infra: Azure, AWS, Docker, Kubernetes, Terraform (optional)
• Testing: xUnit/NUnit, MSTest, Jest (for frontend), Postman, Pact/Contract testing
• Security: OAuth2, OpenID Connect, JWT, API security best practices
• Tools: Git, GitHub Actions, Azure DevOps, Jenkins, Swagger/OpenAPI, EF Core, Dapper, AutoMapper

• Designed a multi-tenant ASP.NET Core Web API with clean architecture, enabling rapid onboarding of new services and scalable data isolation.
• Implemented a Spring Boot microservices suite with centralized configuration and distributed tracing for observability.
• Built a Next.js frontend with API Routes connected to a NestJS backend, delivering a seamless developer experience and robust security model.
• Migrated a legacy monolith to a microservices ecosystem with event sourcing and CQRS where appropriate.
• Implemented Blazor Server/WASM components for rich admin dashboards with real-time data via SignalR.

• 🧰 Backend System Design and Architecture
• 🧩 API Design, REST/GraphQL, and API Gateway strategies
• 🚀 Microservices & Cloud-native development
• 🧪 Testing Strategy & Quality Assurance
• 🔒 Security Architecture and Identity Management
• 🧭 Tech Leadership, Code Reviews, and Mentoring
• 🎯 Performance Tuning, Profiling, and Optimization

• GitHub: https://github.com/hashimoto22
• Stack Overflow: https://stackoverflow.com/users/10669265/kohei-hashimoto
• LinkedIn: https://www.linkedin.com/in/kohei-hashimoto-b734aa22a/
• Twitter: https://twitter.com/kohei10233202

• While my core strengths have expanded to backend and full-stack leadership, I continue to apply mobile development discipline where needed:
  • Flutter-based mobile apps targeting Android, iOS, Web, and Windows
  • State management with Bloc, Riverpod, Provider
  • Firebase integration, in-app purchases, maps, payments, and offline-capable features
  • Cross-platform packaging and deployment considerations

If you’d like, I can tailor this profile further to specific roles, emphasized tech stacks, or particular achievements. I can also draft a concise professional summary for LinkedIn or a resume, and generate a portfolio of sample projects with technical details and outcomes. Would you like me to draft a polished resume version or a LinkedIn-ready summary?