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Backend Developer

We are looking for a Backend Developer to join the Supplier onboarding and Quote Management teams and work directly on the computational core of our platform.

You will write Python and/or dotnet every day. You will work on an existing Python/C# backend and create new services. You will solve real-world business problems, such as creating a constraint optimization engine, working on integrations with our partners, and creating and maintaining internal tools.

The core of the role sits at the intersection of three things

- Algorithmic implementation – translating complex commercial requirements into deterministic, auditable logic. Implement and maintain the optimization engine that drives quote generation.
- API design and contract maintenance – defining clear contracts, ensuring clean, versioned interfaces for downstream consumers.
- Code quality and engineering discipline – making code production-ready, scalable; writing tests, applying engineering standards, ensuring codebase can grow.

You will work directly with the innovation and commercial teams. This role is also designed with growth in mind – the knowledge and context you build here will be a stepping stone toward a technical execution role.

Key Responsibilities

Business Logic Implementation

- Implement and maintain business logic for the quote engine, partner integrations and internal services: supplier selection, service bundling, routing rules, product validation …
- Explore, document and integrate heterogeneous external data sources necessary to the execution of business logic.




- Ensure all outputs are auditable, and explainable to commercial stakeholders.
- Validate model outputs against historical data; measure and report on prediction reliability.
- Optimize the operational value of the integrations with our partners.

API Design & Contract Maintenance

- Define contracts, manage versioning, and ensure downstream consumers are never broken silently.
- Write clear, well-documented API interfaces with explicit input/output contracts and error handling.
- Coordinate with the Platform engineer on service integration and ensure clean separation of concerns between components.
- Maintain API documentation as a living artifact, not an afterthought.

Code Quality & Engineering Practices

- Refactor and clean up existing Python/C# code: reduce complexity, increase testability, bring to production standards.
- Write unit and integration tests that provide real confidence.
- Apply Git, code review, and CI practices to all work.
- Document non-obvious logic thoroughly so knowledge is transferable.

Collaboration & Communication

- Partner with the Commercial teams and the Quote Engine lead Platform engineer – collaborative work, not ticket execution.




- Participate in sprint reviews, propose approaches, and flag risks early.

Requirements

Must-Have

- Advanced Python – non-negotiable. Clean, tested, reusable code.
- API design and implementation; designing and maintaining REST APIs with clear contracts, versioning, and proper error handling.
- Software engineering discipline: testing, code review, Git, and habits of maintainable builders.
- Comfort working in a mixed-language codebase (Python/C#); can read and understand integration points.

Strong Plus

- C#: quality, clean, testable code in C#.
- Familiarity with AWS services (Lambda, API Gateway, S3) or equivalent.
- Experience with API specification tooling (OpenAPI/Swagger, Pydantic, etc.).
- Exposure to Python packaging, dependency management, and CI pipelines.
- Familiarity with constraint-solving tools such as OR-Tools, PuLP, or equivalent.
- Experience in a B2B SaaS, telecom, or logistics context where algorithmic correctness has real commercial stakes.
- Comfort with performance profiling and optimization in Python.

Benefits

- Part of a team that owns the work with direct commercial stakes.
- Direct access to production systems, real data, and decision-makers.
- Exposure to cutting-edge technologies and large-scale integral networks.
- A role designed with trajectory in mind; knowledge builds applicable to senior technical execution path.
- Competitive compensation.
- Pension Plan.
- Hybrid Working.
- 25 days holiday.

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Postúlate en Kit Empleo: kitempleo.es/empleo/6n5qma

📌 Senior Backend Developer (Python) (Barcelona)
🏢 Expereo
📍 Barcelona