Senior C# .NET Backend Engineer - API & SQL | Madrid

Client Server Limited; Humanes de Madrid; Hybrid; EUR 72,000 - 88,000; Full time

Benefits offered by this job

Salary to €80,000

Bonus

23 days holiday, rising to 28 + your生日

Pension

Life Assurance

Income Protection

Critical Illness Cover

Healthcare

Hybrid working

Career development

Job summary

Client Server Limited is hiring a Software Developer / Engineer in Madrid. You will design and implement robust backend services using C# .Net Core, build production APIs, and optimize SQL databases.

The role involves technical ownership, and you’ll work within a small team to modernise systems and deliver new capabilities. Outcomes include hands-on API development, system design for microservices, and production use of AWS.

Qualifications

• Strong C# .Net Core backend development experience
• Experience building production APIs
• Good SQL skills
• Experience with system design, software architecture, microservices and event-driven systems
• Experience with cloud infrastructure in production; AWS preferred
• Experience mentoring engineers and sharing technical knowledge
• Hands-on experience using AI coding / development tools such as Claude or Copilot
• Finance / payments experience is desirable, but not essential
• Fluent English language skills

Responsibilities

• Design and implement robust, scalable APIs and backend services using C# .Net Core
• Lead delivery of new features and contribute to evolving architecture
• Mentor engineers and promote best practices
• Collaborate with cloud and AI tooling to boost productivity

Skills

C# .Net Core

Backend APIs

SQL

System design

Microservices

Event-driven

AWS

Mentoring

AI tools

English fluency

Tools

Claude

Copilot

Job description

Client Server Limited is hiring a Software Developer / Engineer in Madrid. You will design and implement robust backend services using C# .Net Core, build production APIs, and optimize SQL databases.

The role involves technical ownership, and you’ll work within a small team to modernise systems and deliver new capabilities. Outcomes include hands-on API development, system design for microservices, and production use of AWS.