Backend Developer (all genders)

You develop backend functions that reliably represent business processes. This includes data models, APIs, permissions and connecting existing systems. When developing a new function, you also consider migrations, error handling and operations after the release.

A SaaS backend processes orders while multiple users trigger changes and external systems resend messages. You model transactions and idempotency so that results remain consistent. Authorisation checks must apply to every relevant access. For database migrations, you plan compatibility and rollback paths. API tests also cover interrupted operations, invalid state transitions and access to other tenants' records.

• Develop APIs and business services; define interface contracts, input validation and understandable error responses.
• Plan data models and migrations and safely handle transactions, concurrency and repeated requests.
• Implement authentication, role-based access and integrations with third-party systems.
• Add automated tests, meaningful logs and metrics; address performance issues using reliable data.
• Develop idempotent API endpoints and transactional processing with controlled state transitions.
• Measure queries, indexes and API runtimes and verify tenant boundaries automatically.

What matters is demonstrable experience that is relevant to the role. It may come from appropriate vocational training, a degree, professional practice or a well-founded career change. We will align the specific level of responsibility with your knowledge and experience.

• Practical backend experience with an established language and an appropriate framework.
• Confident use of relational databases, HTTP APIs and automated tests.
• Understanding of access control and a service's responsibility within the overall system.

This knowledge is helpful, but you do not need to have all of it at once. In your application, describe where you have already gained practical experience and which areas you would like to explore in greater depth.

• Experience with messaging, distributed systems or SaaS tenant isolation.
• Knowledge of container operations, observability or legacy integration.

You deliver maintainable functions whose behaviour remains transparent under failure conditions and heavy load. Documented APIs and tests help other teams integrate changes without avoidable surprises.

This role can be based in Cologne or performed remotely. We will agree the specific form of collaboration, project requirements and any necessary customer appointments before you start.

This role is offered as permanent employment on a full-time or part-time basis. We will agree the responsibilities, working hours, start date and compensation to suit the role and your level of experience.

Show us in your application which experience or interests you bring to this role. A CV and relevant project examples, certificates or work samples will help us assess your professional background. Please do not send confidential customer data, credentials or protected source code.

Tell us your preferred working model, your possible start date and whether you would like to work full-time or part-time.

If you have questions about the role, contact our recruitment team at hr@otoko.com. Inclusion in the applicant pool is voluntary and takes place only with separate consent; it is not a prerequisite for reviewing your application.