OpenAPI Experts in Berlin
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Meet FRATCH Experts in Berlin, who have recently used OpenAPI
Rüdiger S.
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.
Murad H.
Last position:
Founder & Technical Lead at Hubpoint.Ai
- Founded an AI-powered scheduling and business-management SaaS for SMBs, owning technology strategy, architecture, product development, UX, billing and go-to-market execution.
- Architected and shipped a multi-tenant platform with REST APIs, RBAC, CRM, billing and notifications, powering the manager dashboard, admin console, booking experience and iOS/Android applications.
- Led and mentored 7 software engineers, 1 DevOps engineer, 1 QA engineer and 1 UX/UI designer, while remaining hands-on across backend, frontend and product delivery.
- Built AI voice and chat agents using Python/FastAPI, OpenAI and Anthropic APIs, RAG, pgvector and tool calling; integrated Twilio, Google Calendar/Meet, Stripe and Firebase.
- Owned production infrastructure and automated delivery across separate environments using Docker, Nginx, GitHub Actions and Grafana; represented the company at accelerators and international startup events.
Selected stack: Python, FastAPI, Node.js, Vue 3, React/Next.js, React Native, PostgreSQL, Redis, Docker
Muzamal A.
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 H.
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 B.
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
Toralf C.
Last position:
IT Consultant in PKI Software Development at BWI
- Implementation of a full-stack application with Angular as the frontend framework and Java as the backend language
- Use of the Swagger OpenAPI specification for REST communication between the frontend and backend applications
- Control of a card printer via the Nexus Card SDK framework
- Design and implementation of card management software with a web interface and a JavaFX module for printer monitoring
- Use of Cucumber tests for test automation and creation of test artifacts to test outside the development environment
- Use of Wireshark for network investigations to analyze the API of a third-party product and to monitor the REST API of the self-developed software
Ursula R.
Last position:
Sabbatical with Training at Own Sabbatical
Qaiser A.
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 K.
Last position:
Freelance Software Developer
Karthikeyan R.
Last position:
Full-Stack Developer — Own Product at Self-employed
Java 21 · Spring Boot 3 · Keycloak · PostgreSQL · Docker · Nginx · GitHub Actions · DigitalOcean · React 18 · TypeScript · Plasmo
- Architected and shipped a production-ready Job Application Tracker end-to-end: REST API with 5-stage workflow, pagination, sorting, and dynamic filtering — full ownership from design to live cloud deployment on DigitalOcean.
- Implemented production-grade identity management: OAuth 2.0 / OpenID Connect / JWT / RBAC via Keycloak, applying Hexagonal Architecture and DDD principles.
- Built automated CI/CD pipeline (GitHub Actions); containerised with Docker; Nginx reverse proxy with path-based routing and SSL termination.
- Developed a Chrome Extension (Plasmo framework, Manifest V3) that auto-fills job applications directly from LinkedIn into the tracker — demonstrates full product thinking across backend API and browser client.
Mohamed K.
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
Olaf N.
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
Marcus K.
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
Deependra P.
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 F.
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
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 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
94% (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
79% (Germany: 93%)
Based on our profile pool as of 19 Sep 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 19 Sep 2026. Actual rates may vary depending on seniority level, experience, skill specialization, project complexity, and engagement length.
OpenAPI 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 (100%)
- Banking and Finance (46%)
- Automotive (38%)
- Education (38%)
- Professional Services (38%)
- Energy (33%)
- Healthcare (33%)
- Media and Entertainment (33%)
Please note that freelancers can work across multiple industries, so percentages overlap.
About the technology
API Contracts
OpenAPI is a standard for describing HTTP APIs in a machine-readable format. Teams use it to define endpoints, parameters, request bodies, responses, authentication and error models before or alongside implementation. A well-maintained specification becomes a shared contract for product, engineering, quality assurance and partner teams.
Design and Delivery
OpenAPI supports contract-first and code-first API work. Specialists create or review specifications, resolve naming and versioning decisions, and keep contracts aligned with real services. They also connect specifications to generated clients, server stubs, validation rules and release documentation.
Tools and Ecosystem
The specification works across languages and frameworks rather than belonging to one vendor. Common surrounding tools include Swagger UI, Swagger Editor, Redoc, OpenAPI Generator and validators used in CI pipelines. Strong professionals understand YAML and JSON, HTTP semantics, REST conventions, schema composition and security schemes such as OAuth 2.0 and API keys.
Where It Fits
- Public APIs for customers, partners and mobile applications
- Internal service contracts in distributed systems
- Automatic reference documentation and client generation
- API governance, linting and backward-compatibility checks
- Test design for requests, responses and failure cases
OpenAPI is useful wherever several teams or systems need a dependable view of an API. In Berlin, it appears across software products, financial services, mobility, commerce and public-sector work, with collaboration often split between local teams and remote specialists.
When to Bring Expertise
Companies bring in freelance OpenAPI specialists when an API is being redesigned, published, integrated or placed under stronger governance. Typical signals include incomplete documentation, inconsistent schemas, client-generation failures, unclear ownership or breaking changes reaching consumers. A specialist can audit existing contracts, establish rules and leave practical templates for the internal team.
What Good Looks Like
Strong professionals treat the specification as part of the product, not as an afterthought. They test examples against live behavior, model edge cases, explain trade-offs and make changes traceable through version control. They also know when OpenAPI is not the right abstraction, how to document asynchronous interactions separately, and how to align API design with security, observability and deployment practices.
Frequently asked questions
Curious about OpenAPI? Here are the answers that come up again and again.
OpenAPI is used to describe HTTP APIs in a structured format that people and tools can understand. It supports documentation, validation, contract testing, code generation and communication between teams. A specialist can help turn an informal API into a clear, maintainable contract.
OpenAPI describes HTTP APIs, often built around REST resources and explicit endpoints. GraphQL uses a query schema and a single access model, while gRPC commonly relies on Protocol Buffers and remote procedure calls. The right choice depends on client flexibility, transport needs, performance goals and the systems that must consume the interface.
A strong OpenAPI specialist usually understands HTTP, REST design, YAML, JSON Schema, authentication and version control. Useful adjacent skills include API gateways, CI pipelines, automated testing, Swagger UI, Redoc and OpenAPI Generator. Experience with the project’s implementation language also helps keep the contract aligned with running services.
The required depth depends on the work. A documentation cleanup may need focused specification and tooling knowledge, while an API platform initiative requires judgment around modeling, governance, compatibility and security. For either scope, ask for evidence of contracts that stayed accurate as services and consumers changed.
OpenAPI work is often well suited to remote collaboration because specifications, reviews and tool configuration live in shared repositories. On-site sessions can still help with domain discovery, API design workshops or alignment across Berlin-based teams. Clear written decisions and regular review sessions matter more than constant physical presence.
A good OpenAPI specification is consistent, complete and usable by both people and tools. Check whether examples validate, responses include meaningful errors, security requirements are explicit and generated documentation matches actual behavior. Reviewers should also look for clear naming, reusable schemas and a versioning approach that protects existing consumers.
OpenAPI mainly describes request-response HTTP APIs, so it may not express event flows as completely as a dedicated event specification. Teams often use AsyncAPI for message-driven interactions and keep the two descriptions connected through shared domain models and governance. A specialist should identify that boundary rather than force every interaction into an HTTP contract.
Before starting OpenAPI work, clarify whether the project follows contract-first or code-first practices, which version of the specification is required and where the source of truth lives. Also confirm the target consumers, generation tools, CI checks, authentication model and release process. These details determine whether the deliverable is a document, a governed workflow or a broader API improvement.
The average hourly rate of freelancers in Berlin, Germany who have used OpenAPI in their recent projects is 90 €, which corresponds to a daily rate of about 716 € based on an 8-hour working day.
Of the freelancers in Berlin, Germany who have used OpenAPI in their recent projects, 94% 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 years.
The most common languages among freelancers in Berlin, Germany who have used OpenAPI in their recent projects are German (92%), English (88%), and Spanish (8%).
The most common industries among freelancers in Berlin, Germany who have used OpenAPI in their recent projects are Information Technology (100%), Banking and Finance (46%), and Automotive (38%).
The most common business areas among freelancers in Berlin, Germany who have used OpenAPI in their recent projects are Information Technology (96%), Product Development (92%), and Quality Assurance (63%).
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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FRATCH CEO
