REST API Experts in Dusseldorf
matched in minutesHire experts who design resource-based interfaces, secure integrations and scalable services with REST API, OpenAPI and OAuth. Get precise access to vetted, available freelancers who fit your project, stack and collaboration model.
Meet FRATCH Experts in Dusseldorf, who have recently used REST API
Emre S.
Last position:
IT Project Manager | SAP E-Invoicing Outbound at Rohde & Schwarz
Project: Introduction of statutory-compliant electronic invoicing (outbound, Germany) in SAP for an international technology group.
- Project management: Planning, steering and reporting of the E-Invoicing outbound rollout across all affected business areas, including budget and resource coordination.
- UAT: Structured user acceptance test with key users per business area, test cases per invoice scenario, and consolidated test results for decision making.
- Defect management: Handover and tracking of defects in Jira, including validation of the generated invoices against the statutory schemas.
- Cutover, go-live and hypercare: Readiness checks and cutover planning aligned with the statutory deadlines, coordination of go-live and stabilization during hypercare.
- Stakeholder management and reporting: Alignment with Finance, Tax, business departments and IT, preparation of status reports and decision papers, and consistent follow-up of open items.
- Change management and documentation: Communicated process changes to the business departments, enabled key users, and created process and compliance documentation to ensure traceability and audit readiness.
Marijn S.
Last position:
Senior Software Engineer at Puls Security GmbH
Optimizing and acceleration of our Gitlab CI pipeline
Conceptual work for the PoC of the Zero Trust system
Extension of the policy-engine backend in Go
Extension of the policy-testing mechanism in Python
Architectural design of the PEP component of Zero Trust
Documentation of the product
Technologies: Zero Trust, Go, Python, Gitlab CI, Docker, JWT, Domain-Driven Design
Boris S.
Last position:
Generalist expert for software development at Mercor
- Training AI models, evaluating images and text UI/UX, turning the provided data into insights through OpenAI Feather as part of the machine learning workflow
Technologies: OpenAI Feather
Anupriya P.
Last position:
Senior Software Engineer at Telefonica Germany
(Maternity/Parental Leave: July 2023 – Aug 2024)
- Domain: Payment Domain | Client: Telefonica Germany
- Project: General Payment Service
The General Payment Service is responsible for processing of online payments via external payment service provider like Safer pay and PayPal
- Developed Design of Use (DOU) and interface contract documentation, ensuring clarity and compliance across system integrations
- Designed and delivered REST/SOAP web services with Spring Boot and Spring Data JPA, publishing Swagger contracts through WSO2 API Gateway to improve accessibility and governance.
- Spearheaded the on-premises to AWS Cloud migration, re-platforming from Oracle to PostgreSQL on AWS RDS and deploying services on EC2, improving scalability and cost efficiency.
- Containerized microservices using Docker and orchestrated deployments with Kubernetes, streamlining deployment pipelines and improving system reliability.
- Implemented proactive monitoring and logging via AWS CloudWatch and Kibana, ensuring stability and performance during cutover.
- Enhanced collaboration through code reviews and peer reviews, promoting maintainability and clean coding standards.
- Strengthened quality by writing comprehensive JUnit tests and preparing detailed test cases enabling early defect detection
- Delivered automated API testing with Ready API, Postman, and SOAPUI, and conducted performance testing with JMeter, ensuring reliability in high-transaction environments.
Thorsten L.
Last position:
Senior Security Analyst
- Analysis and remediation of security vulnerabilities in a risk assessment system for energy trading
- System analysis
- Threat modeling
- Decision-making on vulnerability mitigation strategies
- Implementation of vulnerability detection mechanisms
- Security scans
- DevSecOps practices
- Technical environment: Visual Studio Code, JetBrains Suite, MS Threat Modeling Tool, DevSecOps, Git, AWS, DynamoDB, SQL Server, Endur, Snowflake, Orca
- Languages: C#, JavaScript, TypeScript, Python, PowerShell, Bash, Terraform, SQL
Olaf R.
Last position:
DevOps Architect / Consultant at Authority with increased security requirements
- Identification of requirements (legal, organizational, and technical)
- Design of solution architectures
- Evaluation of concepts and technologies
- Preparation of decision templates
- Architectural Decision Records (ADR)
- Coordination of implementation
- Review of implementations
- Documentation
Klajdo F.
Last position:
Independent Product Developer / Software Architect at rastr.eu
- Architected and deployed a live B2B geocoding and demographic-data platform for Germany, combining address lookup with census-based population statistics through a web application and REST API.
Andreas G.
Last position:
Senior Fullstack .NET (Core) & Angular Developer at IT Service Provider
- Supporting several agile teams in the new product development of an enterprise CRM and ERP application
- Web frontend development with Angular 17–21 (microfrontends, Domain-Driven Design, MDB-Bootstrap)
- Backend development with C# and .NET 7–10, MongoDB, MassTransit, RabbitMQ, Entity Framework Core, ElasticSearch (microservices, DDD)
- Technical feature design for assigned tasks
- Technical architecture design including forward-looking planning of AI-supported extension options
- Proof-of-concept implementation of AI-supported workflows with n8n and a locally hosted LLM (Ollama)
- Coordination with stakeholders and Product Owners, support with sprint planning
Result: Delivery of production-ready microservices and frontend modules in agile sprint cycles.
Environment: .NET 7–10 · Angular 17–21 · C# · TypeScript · OpenAPI · Microfrontends · DDD · Kubernetes · Docker · Helm · MS SQL Server · PostgreSQL · MongoDB · MassTransit · RabbitMQ · EF Core · ElasticSearch · Kibana · Azure DevOps · KeyCloak · n8n · Ollama
Ramzi A.
Last position:
Full Stack Java Developer at ISO Public Services GmbH
- Contributed to the development of an advanced RAG AI Chat application that integrates multiple LLM models, enabling users to seamlessly switch between models based on specific tasks. This improved the user experience by providing tailored, efficient solutions for various use cases, such as event scheduling, booking systems, and complex task management.
- Participated in designing and implementing a robust backend architecture using Spring AI, enabling advanced AI-driven capabilities like intelligent task automation, language processing, and contextual recommendations. Leveraged Spring AI Tools and Advisors to enhance the performance and decision-making of the AI models.
- Collaborated on the integration of vector databases to support embeddings, enhancing the app's ability to understand user queries and perform actions based on complex, real-time data inputs.
- Contributed to the development of a seamless, user-friendly front-end interface using React with TypeScript support, ensuring a modern, responsive, and scalable user experience across platforms.
- Assisted in implementing state management with Redux RTK for efficient data flow and real-time updates, optimizing the overall user experience in dynamic scenarios such as scheduling and task management.
- Partnered with stakeholders to define feature requirements, helping ensure that the app could scale to meet evolving business needs and integrate with other systems like calendar and email services. Worked alongside cross-functional teams, including data scientists and UI/UX designers, to fine-tune AI models and ensure alignment with project goals.
- Contributed to ensuring end-to-end system performance, security, and compliance by helping integrate authentication mechanisms, role-based access control, and secure communication protocols in both backend and frontend layers.
Technology Stack and Key Contributions:
- Java / Spring Boot / Spring AI: Developed backend services leveraging Spring AI for intelligent responses, task automation, and complex workflows.
- React / TypeScript: Built intuitive user interfaces with React and TypeScript, ensuring a smooth and scalable frontend.
- Redux RTK: Managed application state with Redux RTK for optimized state management, enabling dynamic, real-time data updates.
- Vector Databases: Integrated vector databases (pgVector) for embedding support, improving AI model performance in handling complex queries.
- PostgreSQL / Redis: Managed persistent and temporary data with relational and in-memory data stores, ensuring data integrity and speed.
- Kafka: Utilized Apache Kafka for event-driven communication and seamless integration between microservices.
- Spring Security: Ensured the security of backend services with robust authentication and authorization mechanisms.
- CI/CD & DevOps: Integrated continuous integration and deployment pipelines to ensure rapid and secure deployment of features and updates.
Ingo K.
Last position:
Co-Founder & Managing Director at Elterngeld Buddy GmbH
- Responsible for the entire software architecture of the parental allowance portal
- iOS and Android app with React Native and Expo, incl. push and OTA updates
- Store releases via App Store Connect and Google Play Console
- TypeScript monorepo for app, website and backend, web with Next.js and Tailwind
- Own promo, voucher and discount engine with contact and segment logic
- Payments via RevenueCat and in-app purchases, authentication with BetterAuth
- REST APIs based on OpenAPI, PostgreSQL with Prisma and Drizzle
- Self-hosting on Hetzner with Docker, Coolify, Terraform and GitHub Actions
- Tests with Vitest, Playwright and visual regression via Chromatic
- Observability via Grafana Cloud and error tracking with Sentry
- Performance marketing via Meta Ads, measured with custom event tracking
- Grew the product to 20,000 app users with a purchase rate of almost 12 %
- Managing Director since 04.2025, responsible for product and technology
Dmitry T.
Last position:
Web Software Engineer at Freelancer
Third-side integration development (REST: Amazon, OpenAI, Etsy, Shopware, Prestashop, etc)
Performance optimization (Refactoring, SQL analysis)
LMS development and deployment (Moodle)
Cloud deployment automation (Amazon, Azure, Gitlab CI/CD, Docker)
Backend and Frontend development (Laravel, VueJs)
Collaboration with partner-developers (national and international)
Shirtigo GmbH
GRELLARTIG Digital GmbH
velpTEC edutainment GmbH
Marc S.
Last position:
Fullstack Developer at PLANT-MY-TREE
PLANT-MY-TREE®-per-order
The application enables Shopify merchants to automatically place tree-planting orders for every incoming order. By integrating ecological contributions directly into the purchase process, the manual effort for tracking and billing reforestation initiatives is eliminated. The system increases transparency for end customers through real-time visualizations of the ecological impact directly in the storefront. The architecture is based on a modular monolith with Spring Boot in the backend and an integrated React app inside the Shopify admin area. The solution uses webhooks to capture order data in an event-driven way and integrates the weclapp ERP system for automated monthly invoicing. An app proxy mechanism provides dynamic statistics such as CO2 compensation and planted trees without any performance loss for the merchant shop.
Tasks:
- Design of the modular software architecture based on Spring Modulith to ensure high maintainability
- Development of the event-driven business logic for evaluating Shopify orders via webhooks
- Implementation of automated invoicing by connecting the weclapp REST API
- Building the frontend using React Router and Shopify App Bridge for native integration
- Design of the database model and implementation of the persistence layer with JPA/Hibernate and Prisma
- Integration of internationalization processes for global use in the frontend and email communication
- Automation of deployment processes using Docker and GitLab CI/CD
Project skills: Java 25, Spring Boot, Spring Security, Spring Modulith, Hibernate, JPA, REST API, PostgreSQL, Maven, Liquibase, React, TypeScript, React Router, Vite, Node.js, Prisma, Zod, Docker, Docker Compose, GitLab CI/CD, Shopify CLI, Shopify App Bridge, Polaris, weclapp, i18next, Lombok, Vitest
Stanislaus S.
Last position:
Security Consultant at Rohde & Schwarz AG at Star Labs GmbH
- Worked on FPGA enhanced network encryption device with secure boot, TPM2.0 and smart card integration for BSI approved usage with Post Quantum Cryptography
- Developed and audited Linux drivers
- Collaborated using GitLab, Gerrit, Confluence and Jira
- Technologies: C, C++, Secure Boot
Younes H.
Last position:
Senior Backend Developer at PTA
- Development and maintenance of database-driven applications for managing supplier and food contracts, with extensive use of Oracle PL/SQL for complex business logic and data processing
- Optimization of PL/SQL procedures, functions, and triggers to ensure the performance and scalability of Oracle database solutions
- Ensuring compliance with best practices in PL/SQL development and implementing standards for code quality and data integrity
- Close collaboration with backend and frontend teams to ensure smooth integration between the Oracle database, C#-based APIs, and Azure cloud services
Alexander R.
Last position:
Business Analyst at Financial Services Provider Landesbank
The Helaba ATLAS project aims to modernize core systems and make them future-proof. As part of the subproject, the existing legacy system for international payments is being replaced by a modern web-based application.
- Analysis of functional and technical requirements
- Analysis and optimization of business processes
- Process modeling
- Preparation and facilitation of workshops
- Defining project scope and prioritizing requirements
- Business process management (analysis, modeling, and optimization)
- Specification of user stories
- Designing business and authorization concepts
- Testing and acceptance
- Designing mockups in Figma
- Creating the UI/UX style guide for web applications Approach: Scrum (agile) Technologies: Jira, Confluence, MS Teams, Conceptboard, Java, Vaadin, Figma
Discover over 15,000 top freelancers
Statistics of experts using REST API
Aggregated from the professional profiles of matched freelancers.
Experience
17 years
Position duration
2.2 years (Germany: 2.9 years)
Positions per freelancer
12
Top business areas
Information Technology, Product Development, Operations
Top industries
Information Technology, Banking and Finance, Retail
Certification focus areas
Information Technology, Project Management, Product Development
Bachelor's degree or higher
96% (Germany: 92%)
Master's degree or higher
63% (Germany: 55%)
Doctorate
13% (Germany: 7%)
Certifications per freelancer
7 (Germany: 3)
Most common languages
German, English, French
Speak two or more languages
97%
Based on our profile pool as of 29 Oct 2026.
Daily rate distribution
The chart shows how the daily rates of experts in this technology in Dusseldorf are distributed, based on recent contracts on our platform. Each bar covers a rate range — its height shows the share of experts charging within that range.
Average rates of experts in Dusseldorf using REST API
Rates are based on recent contracts and do not include FRATCH margin.
The average daily rate is the mean of all daily rates from recent contracts of comparable freelancers on our platform.
The median daily rate is the middle value of all daily rates — half of comparable freelancers charge less, half charge more. Unlike the average, it is barely affected by outliers.
Calculated based on our freelancers’ daily rates as of 29 Oct 2026. Actual rates may vary depending on seniority level, experience, skill specialization, project complexity, and engagement length.
REST API experts industry focus
See which industries our matched freelancers work in most often — every figure is calculated live from the freelancers on FRATCH.
- Information Technology (94%)
- Banking and Finance (50%)
- Retail (50%)
- Telecommunication (44%)
- Transportation (41%)
- Manufacturing (41%)
- Government and Administration (38%)
- Education (28%)
Please note that freelancers can work across multiple industries, so percentages overlap.
About the technology
What REST API does
REST API is a widely used way to let software systems exchange data over HTTP. It models business resources such as users, orders or products and exposes clear operations for reading, creating, updating and deleting them. JSON is common, but other representations are possible.
Where it is used
REST API specialists deliver interfaces for web applications, mobile products, partner integrations and internal services. Typical work includes:
- Designing resource structures and endpoint conventions
- Connecting frontend applications to backend services
- Integrating payment, identity, logistics or data providers
- Modernizing legacy interfaces without disrupting consumers
Ecosystem and tooling
Strong REST API work combines HTTP semantics with practical ecosystem tools. Professionals often use OpenAPI or Swagger for contracts and documentation, Postman for exploration, and automated tests in the project’s language and framework. OAuth 2.0, JSON Web Tokens, gateways, caching and observability also matter in production.
When companies need help
Freelance expertise is useful when an interface must be designed before several teams build against it, or when existing endpoints are inconsistent, slow or difficult to secure. It is also valuable during service decomposition, external system integration and migrations from tightly coupled applications. In Dusseldorf, specialists may support local teams on-site, remotely or in a hybrid setup, with English or German collaboration depending on the project.
What quality looks like
A reliable REST API has predictable URLs, meaningful status codes, validation, pagination and clear error responses. Strong professionals define versioning and compatibility rules before changes reach consumers. They also consider rate limits, idempotency, access control, performance and useful documentation rather than treating the interface as a thin layer over a database.
Skills beyond endpoints
The best specialists understand the systems behind an API and the clients that depend on it. Look for experience with databases, authentication, cloud deployment, CI/CD, testing and monitoring, plus the ability to explain trade-offs to product and technical stakeholders. Before engaging someone, review API contracts, test coverage, security decisions and evidence that integrations remain stable as requirements change.
Frequently asked questions
Before you brief your next project: the most common questions about REST API.
A REST API lets applications exchange data and trigger actions through HTTP requests. Companies use it to connect web and mobile interfaces with backend services, expose capabilities to partners, and link systems such as commerce, identity, payment and logistics software.
A REST API usually exposes resources through several predictable endpoints, while GraphQL lets clients request a tailored data shape through a query model. SOAP uses a stricter message and contract style and remains relevant in some enterprise environments. The right choice depends on client needs, governance, existing systems and integration constraints.
A strong REST API specialist should understand HTTP, data modeling, databases, authentication and automated testing. Useful adjacent skills include OpenAPI, OAuth 2.0, API gateways, cloud deployment, CI/CD, logging and monitoring. Knowledge of the backend and frontend stacks improves decisions about contracts and compatibility.
The required expertise depends on the scope and risk of the interface. A simple internal integration may need focused implementation skills, while a public or business-critical API calls for careful security, versioning, documentation, resilience and support planning. Assess the complexity of the consumers and data flows rather than relying on a generic experience threshold.
Yes. REST API work is well suited to remote collaboration when teams maintain clear interface contracts, shared documentation, code review and test environments. Dusseldorf-based companies can combine remote delivery with on-site workshops when domain knowledge, stakeholder alignment or security requirements make face-to-face work useful.
Ask for examples of REST API contracts, integration work and production incidents they have handled. Review how they approach authentication, validation, errors, versioning, monitoring and backwards compatibility. A practical discussion about one of your resources or workflows often reveals more than a list of tools.
A REST API may be less suitable when clients need highly variable data shapes, continuous bidirectional updates or extremely strict enterprise messaging contracts. GraphQL, WebSockets, event-driven interfaces or SOAP may fit those needs better. Many systems still combine these approaches instead of forcing one interface style everywhere.
A quality REST API is easy to understand, secure, test and evolve. Check its OpenAPI documentation, status-code usage, error model, validation, automated tests and monitoring signals. Also test realistic consumer journeys and confirm that changes do not silently break existing clients.
The average hourly rate of freelancers in Dusseldorf, Germany who have used REST API in their recent projects is 89 €, which corresponds to a daily rate of about 709 € based on an 8-hour working day.
Of the freelancers in Dusseldorf, Germany who have used REST API in their recent projects, 96% hold at least a Bachelor's degree, 63% hold at least a Master's degree, and 13% hold a doctorate.
On average, freelancers in Dusseldorf, Germany who have used REST API in their recent projects have 17 years of professional experience, with a single engagement typically lasting around 2.2 years.
The most common languages among freelancers in Dusseldorf, Germany who have used REST API in their recent projects are German (100%), English (97%), and French (16%).
The most common industries among freelancers in Dusseldorf, Germany who have used REST API in their recent projects are Information Technology (94%), Banking and Finance (50%), and Retail (50%).
The most common business areas among freelancers in Dusseldorf, Germany who have used REST API in their recent projects are Information Technology (100%), Product Development (94%), and Operations (56%).
Main locations of FRATCH Experts, who have recently used REST API
Our freelancers and interim experts are at home across the DACH region — available on-site in the major business hubs or fully remote. Choose a location to discover matched specialists, local market insights and up-to-date availability.
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