API Developer

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