OpenAPI Experts in Berlin
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Meet FRATCH Experts in Berlin, who have recently used OpenAPI
Rüdiger Schulz
Last position:
Full-Stack Software Engineer / Consultant for Digitalization at ARTEVENT
Designed, built, and launched an internal event planning web application used by over 100 department leads for a large event, despite having no dedicated testing phase.
Ensured smooth, failure-free operation during first production use, leading to the tool being adopted for future events.
Automated catering calculations and related workflows, significantly reducing email communication and manual computation effort for meal planning.
Managed deployment and hosting on a Linux server using Coolify, including application setup and runtime operations.
Hired and guided a communication designer on UX while independently owning all technical decisions and implementation.
Muzamal Ali
Last position:
Data Scientist / AI Consultant at HelmX
- Delivered AI and data science solutions, including LLM-based chatbots and data pipelines, improving operational efficiency.
- Collaborated on product features, achieving measurable impact and maintaining strong client relationships.
Ibrahim Hilali
Last position:
Senior Full Stack / AI Engineer at Punktum Digital GmbH
- Context: Healthcare and laboratory teams required faster document analysis, treatment-planning support, and reliable AI workflows for MR/VR-assisted operations.
- Contribution: Built the AI healthcare platform, model/agent workflows, VR-glasses deployment platform, REST APIs, Next.js/React interfaces, and CI/CD pipelines.
- Impact: Delivered a production-ready AI product foundation that improved clinical document review, supported laboratory automation, and made VR fleet deployment manageable across environments.
Tech: TypeScript, Next.js, Node.js, React, Java, Spring Boot, Python, PyTorch, TensorFlow, Docker, PostgreSQL, OpenAPI, GitLab, GitHub Actions.
Marcus Brose
Last position:
Alpecin.de - Dr. Wolff Group
- Development of a component library based on a design system for several international brands such as Alpecin, Karex, Linola and Plantur 39
- Integration of headless CMS, PIM and commerce solutions
- UI/UX development
- Prototype development
- MVP development
- API design and development
- SaaS development (whitelabel/multi-tenant)
- Headless CMS integration
- Design systems Digital signage
- Internationalization (i18n)
- Javascript
- Component library
- Tailwind CSS
- Storybook
- HTML
- Vue 3
- Storyblok
- Github Actions
- SEO
- i18n Theming
- React
Ursula Raab
Last position:
Sabbatical with Training at Own Sabbatical
Qaiser Abbasi
Last position:
Freelance Lead DevOps Engineer at Schwarz Gruppe Produktion
Bootstrapping a CloudOps team and building a multi-cloud provider backend for a low-code Internal Developer Platform (IDP) with env zero
Introducing user story mapping, ADRs, milestones, and backlog management
Designing and developing core APIs, setting up CI/CD pipelines, OpenTofu/Terraform scripts
Representing and communicating the team with third-party stakeholders (e.g. env zero)
(Cross-)team coaching on DevOps, software design, Terraform, Golang, and agile practices
Igor Kazarnovskiy
Last position:
Freelance Software Developer
Mohamed Keita
Last position:
Interim Senior Camunda & BPMN Consultant, Spring Boot & Java Backend Developer at GEMA/IT4IPM GmbH
- Subject matter expert for the client on modeling and developing Camunda BPMN 2.0
- Development of new features and APIs, and coordination of tasks
- Design and development of RESTful APIs with Swagger (code first)
- Creation of target designs, high-level concepts, and requirement specifications
- Analysis and evaluation of alternative solution approaches
- Integration of external IT systems (ANUBIS, SES, ZPS) via Google GCP Pub/Sub and RESTful web services
- Pair programming, code reviews, and collaboration with API product owners
- Consulting on transforming legacy BPMN workflows and configuring Camunda BPM
- BPMN and DMN modeling and implementation in short iterations
- Operational support, bug fixing, and knowledge documentation
- Use of TDD, static code analysis with SonarQube, and integration tests
- Automation of test cases in Java and analysis of stack traces/logs on GCP-PROD
- Identification and execution of test data and documentation of test results
Marcus Kühl
Last position:
Senior Software Developer (APEX) at Various
- Further development and tuning of a medium-sized application for managing events and participants
- Identification of bottlenecks
- Adding missing foreign keys and indexes
- Reprogramming views and SQL queries in APEX
- Report development with Jasper Reports
- Mentoring other APEX developers
Olaf Nouvortne
Last position:
Frontend Engineer at Danaher/Hach Lange GmbH
- Developed a SolidJS frontend UI for a spectrometric water analysis system on an ARM-based embedded Linux platform
- Prototyped UI in TypeScript React/Nx with LitElements and MQTT integration
- Built production UI using SolidJS, SUID, i18next, Ajv, MQTT.js, C3.js
- Refined requirements with UX team and water analysis system engineers
- Defined and documented system architecture, MQTT message formats, frontend architecture, and development setup
- Set up frontend system from scratch, implemented domain-oriented type system, UI components, and application state
- Managed MQTT pub/sub services and schema-based message validation in frontend
- Coached two junior frontend developers
- Worked in an agile remote team using JIRA, Git, and Bitbucket
Deependra Pokhrel
Last position:
Data Specialist at Cloud Factory
- As a Data Specialist, I leveraged analytical expertise to transform raw data into actionable insights, driving strategic decision-making and operational improvements. My role encompassed data interpretation, reporting automation, and cross-functional collaboration, utilizing advanced tools such as Microsoft Excel, Power BI, and Python for comprehensive data analysis.
- Implemented Python scripts to validate and reconcile large datasets, reducing manual errors and improving data reliability.
- Utilized Python (Pandas, NumPy, Matplotlib/Seaborn) to automate data cleaning, analysis, and visualization, improving efficiency and accuracy in reporting.
- Developed interactive dashboards in Power BI to present key metrics, trends, and performance indicators, facilitating real-time decision-making.
- Designed and executed automated reports using Excel (Pivot Tables, Power Query, VBA) and Power BI, ensuring data accuracy and consistency across departments.
- Data Analysis: Excel (Advanced Pivot Tables, Power Query), Power BI (DAX, Data Modeling), Python (Pandas, NumPy, Visualization Libraries)
- Automation & Reporting: Power BI Dashboards, Excel Macros (VBA), Python Scripting.
Jens Freudenau
Last position:
Senior PHP Developer at Own Project
- Developing an app that reflects the stock portfolio
- Environment: Laravel 12, PHP 8.4, MySQL, Git, IntelliJ, GitHub, AlpineJs, TailwindCss
Ramu Molankula
Last position:
Software Development Engineer at Olive Crypto Systems Pvt Ltd (National Payments Corporation of India)
Contributed to the development of a UPI simulation system, ensuring alignment with NPCI standards from UAT to production, and achieving a 98% success rate with improved API workflow clarity.
Built a data-driven certification process that increased scenario coverage by 40% and cut certification time to 1 week.
Executed 100+ transaction scenarios for switch testing using a real-time sample bank, achieving 85% accuracy in critical flows and supporting on-time certification for banks.
integrated Spring Boot microservices with RabbitMQ to automate certification workflows, reducing manual efforts by 40%.
Supported the rollout of a global UPI simulation tool used by 20+ international partners to explore real-time remittance APIs and process flows efficiently.
Streamlined certification workflows, reducing integration time by 50% and enabling full API understanding within a week.
Engineered a real-time international remittance simulator and testing framework facilitating API/application flow comprehension for partners like Lyra and TerraPay; cut partner integration time by 40%.
Developed RESTful APIs using Spring Boot and Kafka to simulate high-volume remittance traffic for partner certification.
Collaborated with international partners to optimize API performance, identifying and resolving latency issues, resulting in a 25% reduction in response times during partner integrations.
Shameek Chakraborty
Last position:
Startup Mentor at Zukunft Gründen Agritech ClimAccelerator
- Coaching founders of AI-led agritech and climate tech startups on validation, initial go-to-market and fundraising
Daniel Schlieder
Last position:
DevOps Engineer / Cloud Infrastructure Engineer at ComputerStack GmbH
- Provisioned a Kubernetes platform on Open Telekom Cloud CCE with comprehensive network isolation
- Built a VPC architecture with public, private, and data subnets
- Integrated managed services: RDS PostgreSQL, DCS Redis, DMS Apache Kafka
- Implemented monitoring with Cloud Eye and Log Tank Service
IMPACT: Cloud Infrastructure Engineer delivered a production-ready platform in 5 days with full network security isolation
Discover over 15,000 top freelancers
Statistics of experts using OpenAPI
Aggregated from the professional profiles of matched freelancers.
Experience
19 years
Position duration
2.1 years (Germany: 1.8 years)
Positions per freelancer
11 (Germany: 14)
Top business areas
Information Technology, Product Development, Quality Assurance
Top industries
Information Technology, Banking and Finance, Automotive
Certification focus areas
Information Technology, Project Management, Product Development
Bachelor's degree or higher
92% (Germany: 89%)
Master's degree or higher
31% (Germany: 50%)
Certifications per freelancer
1 (Germany: 2)
Most common languages
German, English, Spanish
Speak two or more languages
76% (Germany: 93%)
Based on our profile pool as of 30 Aug 2026.
Daily rate distribution
The chart shows how the daily rates of freelancers in this technology in Berlin are distributed, based on recent contracts on our platform. Each bar covers a rate range — its height shows how many freelancers charge within that range.
Average rates of experts in Berlin using OpenAPI
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 30 Aug 2026. Actual rates may vary depending on seniority level, experience, skill specialization, project complexity, and engagement length.
About the technology
API contracts OpenAPI is the standard for describing REST APIs in a machine-readable way. It defines paths, request bodies, responses, auth, and schema details so teams can work from one contract. Companies use it to keep backend, frontend, and partner integrations aligned.
What specialists deliver
- OpenAPI Specification files for new and existing services
- Clear API documentation for internal and public use
- Request and response schemas that stay consistent
- Versioned contracts for changing endpoints
Tooling and ecosystem OpenAPI, often called OAS, is commonly used with Swagger tools, editors, validators, and code generators. Strong professionals know how to keep the spec readable while making it useful for testing, client generation, and review workflows. They also understand how to fit it into CI checks and release processes.
When companies bring help Teams usually need freelance expertise when an API has grown without clear documentation, when multiple services must share one contract, or when partner access depends on a stable spec. In Berlin, this often comes up in SaaS, fintech, logistics, and platform teams that work with distributed specialists. Remote work is common, but on-site sessions help when many stakeholders need to agree on the same API rules.
What strong professionals do well A strong OpenAPI specialist writes specs that are accurate, concise, and easy to maintain. They map real service behavior, spot inconsistencies early, and know when to keep design simple instead of over-modeling. They also communicate well with product, backend, and QA specialists.
Quality signals Good work is not just valid YAML or JSON. It is a spec that developers trust, tests can use, and other teams can read without extra explanation. Look for clean naming, reusable components, consistent error handling, and a clear approach to authentication and versioning.
Frequently asked questions
Curious about OpenAPI? Here are the answers that come up again and again.
OpenAPI is used to describe REST APIs in a format that tools and people can read. It helps teams document endpoints, define request and response shapes, and keep client work aligned with backend behavior. It is common in services that need clear contracts, partner integrations, or generated SDKs.
OpenAPI is the current specification name, while Swagger is the older ecosystem name many people still use. In practice, searchers may mean the spec, Swagger UI, Swagger Editor, or related tools. A good specialist should understand both terms and the differences between the specification and the tooling around it.
A company should bring in OpenAPI expertise when API documentation is missing, outdated, or inconsistent across teams. It is also useful when you need a contract for external partners, want reliable code generation, or need to standardize many services. Freelance help is practical when the work is focused and time-sensitive.
A strong OpenAPI professional usually knows REST design, JSON Schema, authentication patterns, and API versioning. They often work with validation tools, mock servers, and code generators. Familiarity with testing and CI workflows is a plus because the spec needs to stay correct over time.
Not every OpenAPI task needs the same depth. A simple documentation cleanup may need someone who can edit and validate a spec, while a large platform needs someone who can design reusable components, error models, and governance rules. The more services and stakeholders involved, the more valuable deeper experience becomes.
Yes, most OpenAPI work can be done remotely because the main output is the spec, not the office location. Remote collaboration works well when the specialist can review services, attend API design sessions, and communicate clearly in English or German. On-site meetings in Berlin can still help during early workshops or stakeholder reviews.
Look at whether the OpenAPI spec matches the real API, not just whether it passes validation. Good work shows consistent naming, reusable components, clear auth definitions, and sensible error handling. The best specialists also explain trade-offs and help teams keep the contract maintainable.
OpenAPI is often compared with gRPC, GraphQL schema design, and ad hoc documentation approaches. The right choice depends on whether the API is REST-based, needs strong contract sharing, or serves external consumers. A good specialist can explain when OpenAPI is the better fit and when another approach makes more sense.
The average hourly rate of freelancers in Berlin, Germany who have used OpenAPI in their recent projects is 87 €, which corresponds to a daily rate of about 698 € based on an 8-hour working day.
Of the freelancers in Berlin, Germany who have used OpenAPI in their recent projects, 92% hold at least a Bachelor's degree and 31% hold at least a Master's degree.
On average, freelancers in Berlin, Germany who have used OpenAPI in their recent projects have 19 years of professional experience, with a single engagement typically lasting around 2.1 years.
The most common languages among freelancers in Berlin, Germany who have used OpenAPI in their recent projects are German (90%), English (86%), and Spanish (10%).
The most common industries among freelancers in Berlin, Germany who have used OpenAPI in their recent projects are Information Technology (100%), Banking and Finance (48%), and Automotive (43%).
The most common business areas among freelancers in Berlin, Germany who have used OpenAPI in their recent projects are Information Technology (95%), Product Development (90%), and Quality Assurance (57%).
Main locations of FRATCH Experts, who have recently used OpenAPI
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.
Hamburg 
Munich 
Cologne 
Frankfurt 
Stuttgart Request a free demo
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Philipp Thomaschewski
FRATCH CEO
