04/21/2026 updated

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Senior .NET Backend Engineer with AI Integration Expertise

A Guarda, Spain
Only remote
Licenciado en Ciencias Matemáticas / BSc Mathematics. Universidad Santiago de Compostela Year: 1999.
A Guarda, Spain
Only remote
Licenciado en Ciencias Matemáticas / BSc Mathematics. Universidad Santiago de Compostela Year: 1999.

Profile attachments

jmcasal-backend-dotnet.pdf

About me

Senior .NET Backend Engineer, 14+ years independent contractor. Multitenant SaaS, regulated financial systems, logistics platforms, LLM integration into production workflows. Mathematics background. Remote B2B contracts only.

Clean ArchitectureLLMDDDAzure DevOpsASP.NETArtificial IntelligenceC Sharp (Programming Language)Entity FrameworkPostgreSQLMicrosoft SQL ServersMongoDBRabbitMQRedisSystems Integration.NET CoreBackendRestful ApiDockerMicroservices
.NET Backend Development C#, .NET 6/8+, ASP.NET Core, Minimal APIs. 20+ years building enterprise backend systems in production: multitenant SaaS, regulated financial platforms (MiFID2), logistics operational systems. Clean Architecture, DDD/CQRS, microservices, event-driven design.

AI Integration LLM integration into production .NET workflows using Claude API. Runtime-configurable behavior — prompts and domain rules externalized, zero hardcoded logic. Agentic pipelines with full auditability.

Data SQL Server specialist: query optimization, indexing strategies, complex T-SQL, schema design under production constraints. EF Core, PostgreSQL, MongoDB.

Cloud & Infrastructure Azure (App Service, Azure SQL, Azure Functions), Docker, Kubernetes, CI/CD. Sole ownership of production systems including infrastructure and operations.

Messaging & Distributed Systems RabbitMQ, Redis. Async messaging between distributed modules and distributed session management in multitenant environments.

Mathematical background Degree in Mathematics (University of Santiago de Compostela). Direct impact on how I design software: precise domain models, explicit invariants, formal reasoning about correctness. I treat complexity as something to be understood and controlled, not worked around.

Track record 14+ years as independent contractor. Sole technical owner on multiple long-running production systems — some running 8-9 years without interruption. No team, no handoff, full accountability.

Languages

EnglishGoodSpanishNative speaker

Project history

Sole Technical Owner

Air Logistics

Transport & Logistics

50-250 team member

Desktop system for air shipment management and billing — in active production for 8+ years without interruption.

- AWB/house management · automated economic valuation
- Rate engine by client and service · calculation rules by operative conditions
- Full traceability to accounting
- Integration with Microsoft Dynamics Navision and external flight systems

Stack: .NET Framework · C# · SQL Server · T-SQL

Sole Technical Owner

Logistics Company

Transport & Logistics

50-250 team member

Full-cycle management system for an air handling operator — designed, built and maintained in production for 4+ years. No team, no handoff, full accountability.

Covers the entire operational backbone:
- Flight and operations management · manifests · tariff engine
- Automated billing · warehousing · accounting export
- Azure deployment and operations

Stack: .NET 5 · C# · ASP.NET MVC · REST API · Azure App Service · Azure SQL · xUnit

Backend Consultant

Fintech

Banking & Financial Services

50-250 team member

Multitenant SaaS platform for regulated financial advisory (MiFID2) — 4 years, multiple modules, production environment.

- Refactoring critical components under production constraints
- Performance optimization and per-tenant observability in a regulated environment
- Modules: account and financial product management, portfolio reporting, advice engine, digital signature and document management

Stack: .NET 6/8 · C# · ASP.NET Core · SQL Server · MongoDB · Docker · RabbitMQ · Redis

AI-Integrated Backend System Developer

Personal project
End-to-end design and development of a production-grade backend system integrating LLM-based analysis into real domain workflows.
  1. .NET 8 · Clean Architecture (Core / Application / Infrastructure / Worker)
  2. Runtime-configurable AI behavior — prompts and scoring rules externalized, zero hardcoded logic
  3. Agentic pipeline with full auditability · Dockerized deployment
  4. Chrome Extension (TypeScript) for data capture · Alpine.js SPA
Stack: .NET 8 · C# · Claude API · SQL Server · Docker · Quartz · TypeScript

Backend Consultant

Banking

Banking & Financial Services

50-250 team member

Backend development on a banking system in active production.

- Security hardening on critical components
- Performance optimization under production constraints
- Focused engagement with direct impact on system stability and response times

Stack: ASP.NET WebForms · .NET Framework 4.7 · C# · SQL Server

Backend Consultant

Automotive Sector

Automotive & Vehicle Manufacturing

10-50 team member

Business analytics platform with microservices architecture and Snowflake-based data layer.

The existing .NET Snowflake connector was incompatible with the client's microservices environment. Solution: forked the official driver and adapted it to resolve the connectivity constraints.

→ github.com/jmcasal/snowflake-connector-net

Stack: .NET Core 3.1 · C# · Docker · Kubernetes · Snowflake · CData

Backend Developer

Hotel Sector

Other

10-50 team member

Backend integration layer connecting hotel websites to a dual reservation system — internal booking engine and HotelBeds (external B2B distribution platform).

- Real-time availability, pricing and reservation flow across both backends
- Consistent data synchronization between internal inventory and external channel

Stack: .NET · C# · REST API · HotelBeds API

Senior .NET Developer

Senior .NET Developer

Goods & Retail

< 10 team member

Supplier purchasing management application with configurable price formula engine.

- Catalog import performance optimization: reduced from 1 hour to seconds on datasets up to 4M references
- Real-time product crawler
- Automated purchasing robot

Stack: .NET Framework 4.5 · C# · SQL Server · Selenium

Full Stack Developer

Retail

Goods & Retail

50-250 team member

Full design and development of a distributed retail management system — built in 5 months, running in production for 9 years.

Custom .NET communication layer for real-time sync across 30+ stores with guaranteed offline operation.

- Decentralized POS · barcode reading · label printing
- Central and per-store inventory management
- Proprietary loyalty engine — points, membership cards, email campaigns
- Web and mobile — customers could reserve items from any device
- Integration with Microsoft Dynamics Navision

Stack: .NET Framework · C# · SQL Server · PostgreSQL · SOAP Services · Navision

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