Interface Consultant REST API (m/f/d), project-related on demand

Project overview

Key Data

Description

For our client, we are looking for an experienced freelancer for system integration and REST API interfaces. Our client continuously implements customer projects where existing systems need to be connected to the respective end-customer's environment, for example to ERP or IoT platforms. An expert is sought who can advise and also implement themselves.

This is not a classic full-time project. We are looking for a permanent contact person who can step into individual customer projects as needed, mostly in the conception and connection phase. Assignments can be planned in advance.

• Start: immediately or November 2026
• Duration: long-term cooperation, project-related assignments as needed
• Workload: flexible, not a full-time project, assignments can be planned in advance
• Location: Remote, on-site appointments by arrangement

Responsibilities

• Record and evaluate technical requirements together with end customers
• Create or contribute to functional specifications or interface specifications
• Design integration architectures between systems from different manufacturers
• Develop, test, and commission REST API connections
• Advise on automation and AI use cases that query and exchange data via interfaces

Requirements

What we offer

Please send us your current profile with availability and hourly rate expectation.

• Several years of experience in system integration and interface development
• Very good knowledge of REST API, JSON, and common authentication methods
• Experience in connecting ERP and/or IoT systems
• Confident interaction with end customers, including requirements gathering
• Experience with communication or telephony solutions is an advantage
• Experience with AI-supported automation is desirable
• Very good German language skills
• Long-term cooperation with recurring assignments
• Varied customer projects instead of a single long-term project
• Direct contact and short decision-making processes

Project details

• Start: 2026-11
• Duration: 12 Monate
• Remote: remote
• Location: Düsseldorf, Deutschland, DE
• Languages: German