API Developer
Keystone Solutions · Brussel, Belgium
Mission Overview:
We are seeking an API Developer for a consultancy mission at a client site, representing Keystone Solutions. The objective is to re-implement a subset of a third-party API to ensure a smooth transition for current users. This role involves working on a straightforward API with two main functional parts: a metadata layer and a submission layer.
Key Responsibilities:
- Analyze the existing API and its documentation, and agree on the subset to cover.
- Analyze the ODS database and map its metadata to what the existing API exposes, identifying any gaps.
- Propose and implement a security approach (authentication, authorization, secure handling of submitted data), highlighting where it differs from the current API.
- Implement the metadata endpoints on top of the ODS database.
- Implement the submission endpoints, with validation of submitted data and meaningful error responses.
- Hand over submitted data to the ODS loading code (or store it in the form that code expects).
- Write automated tests and concise technical documentation.
- Deploy and demonstrate the solution on Ubuntu Linux.
- Report on limitations, open questions, and recommended next steps.
Required Skills:
- Python 3.12+ with FastAPI.
- SQLAlchemy and PostgreSQL (reading and mapping an existing schema).
- REST API design.
- API security: authentication and authorization (e.g. OAuth2/OIDC, JWT, API keys), TLS, input validation.
- Automated testing (pytest).
Nice to Have:
- Polars in combination with SQLAlchemy.
- uv for package management.
- Experience with API compatibility or migration projects.
- Experience handling sensitive data (e.g. health data) and GDPR requirements.
- Linux deployment experience.
Soft Skills:
- Autonomy and ability to work from incomplete documentation.
- Pragmatism: focusing on the critical parts first while keeping quality high on what is delivered.
- Clear communication of findings and limitations.
At Keystone Solutions, we pride ourselves on our consultancy nature, offering dynamic projects that provide turbo-charged learning opportunities. As a
If you are ready to tackle technical and strategic challenges in a dynamic consultancy environment, apply today at Keystone Solutions Career Portal.
Duration: 26/10/2026 - 31/12/2026 3 months • (full time)
Skills required:
- API - Level: Expert - Most recent: Any time
- API Design - Level: Expert - Most recent: Any time
- API Developer experience (SOAP en REST) - Level: Expert - Most recent: Any time
- API development (FastAPI,...) - Level: Expert - Most recent: Any time
- API Security a.d.h.v. OAuth en WS-Security - Level: Expert - Most recent: Any time
- PostgreSQL - Level: Expert - Most recent: Any time
- Pytest - Level: Expert - Most recent: Any time
- Python - Level: Expert - Most recent: Any time
- REST - Level: Expert - Most recent: Any time
- SQLAlchemy - Level: Expert - Most recent: Any time
Language requirements:
Dutch
Level Passive knowledge
English
Level Active knowledge
French
Level Passive knowledge