Senior Full Stack Engineer

Sans Souci; Belfast City District; On-site; GBP 47,000 - 63,000; Full time

Job summary

Sans Souci in Belfast is seeking a Senior Full Stack Engineer to own delivery across client and product work, shaping solutions from conception through deployment.

You’ll work with React, Next.js and modern backend stacks (FastAPI/Node.js), on cloud-native Azure/AWS architectures, including AI-enabled projects. You’ll drive technical decisions, test, deploy and mentor peers, with a clear route to Technical Lead.

Qualifications

• Proficiency with React/Next.js for frontend and FastAPI/Node.js for backend.
• REST API design and API-first development.
• SQL and modern data platforms.
• Cloud platforms (Azure and/or AWS) with serverless architectures.
• Containers and Docker; CI/CD and Infrastructure as Code.
• GitHub and modern development tooling.
• Automated testing and secure development practices.
• DESIRABLE: Experience with LLM APIs or AI agents; Azure AI/OpenAI/AWS AI services.

Responsibilities

• Design, build, and deploy full-stack web applications and APIs
• Work across cloud-native architectures on Azure and/or AWS, including serverless and container-based services
• Contribute to data platforms, workflow orchestration and business process automation
• Apply automated testing, CI/CD and secure development practices throughout delivery
• Support infrastructure-as-code and deployment pipelines across client and internal projects
• Work with the Test Functions to get products release through environments

Skills

Engineering fundamentals

Problem solving

Willingness to learn

Tools

React

Next.js

FastAPI

Node.js

Azure Functions

Docker

GitHub

Serverless

CI/CD

Job description

Sans Souci is a fast-growing digital innovation firm based in Belfast. We are looking for a Senior Full Stack Engineer to join our growing technology team and take on real ownership across our client and product work.

We build increasingly sophisticated digital products, data platforms, AI-enabled solutions and cloud services for clients across the public and private sectors. We need you to do more than take tickets and write code. You’ll need to understand a problem, help shape the solution, make sound technical decisions, build it, test it, deploy it, and support other engineers to deliver well. This is a genuine next step for a Senior Developer ready to grow. There is a clear and fast route to Technical Lead for the right person once you've proven your impact.

Location requirement: This role is open to candidates based in Northern Ireland only.

KEY RESPONSIBILITIES:

Software Delivery

• Design, build, and deploy full-stack web applications and APIs
• Work across cloud-native architectures on Azure and/or AWS, including serverless and container-based services
• Contribute to data platforms, workflow orchestration and business process automation
• Apply automated testing, CI/CD and secure development practices throughout delivery
• Support infrastructure-as-code and deployment pipelines across client and internal projects
• Work with the Test Functions to get products release through environments

AI-Enabled Engineering

• Build and support AI and agentic AI solutions, including LLM APIs and RAG architectures
• Work with tool/function calling, structured outputs and vector databases
• Use modern AI-assisted development tools while maintaining engineering discipline, review and testing
• Evaluate and test AI systems for reliability and accuracy
• Stay current with emerging AI engineering practices and bring them into delivery
• Turn incomplete or evolving requirements into sensible technical solutions
• Explain technical decisions clearly to non-technical stakeholders
• Review other engineers' code and share knowledge generously
• Work directly with clients when required
• Support the wider team in raising engineering standards day to day

ESSENTIAL SKILLS & EXPERIENCE

• React, Next.js or similar modern frontend frameworks
• FastAPI, Node.js or equivalent backend technologies
• REST APIs and API-first development
• SQL and modern data platforms
• Cloud & Engineering Practices
• Azure and/or AWS, including Azure Functions / Durable Functions and serverless architectures
• Containers and Docker
• Git and GitHub
• CI/CD and automated deployment; Infrastructure as Code
• Automated testing and application security / secure development practices

You don’t need to tick every box — we are more interested in excellent engineering fundamentals, strong problem-solving ability and the appetite to learn.

DESIRABLE

• Experience with LLM APIs, RAG architectures or AI agents
• Exposure to Azure AI / OpenAI / AWS AI services
• Experience with evaluation and testing of AI systems
• Comfort reviewing others' code or supporting less experienced engineers
• Interest in eventually moving into a broader technical leadership role

WHY JOIN US

• Work with modern cloud and AI technologies
• Influence technical decisions and engineering practices as you grow
• Experiment with emerging technologies
• Work directly with experienced engineers, colleagues and client teams
• See the software you build solve real-world problems
• Progress quickly to Technical Lead as you prove your impact

Salary: £55,000 annually.

If you’re a strong software engineer who wants more ownership, more variety, and room to grow quickly, we’d like to hear from you.