OpenAPI Experts in Stuttgart
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Meet FRATCH Experts in Stuttgart, who have recently used OpenAPI
Sercan Tatar
Last position:
Co-Founder & Lead Software Architect at Pflege-Pfad
- Focus: system architecture, cloud-native platforms, microservices, API design
- Product: Pflege-Pfad is a digital matchmaking platform that connects relatives of people in need of care directly with verified care services and caregivers - without an agency and without ongoing fees.
- Business analysis & process design:
- Analysis of the German care market and identification of the key pain points of both target groups.
- Modeling of the core business processes: registration, verification, care request, application, placement, and rating.
- Definition of the business model as a freemium/premium model with optional contact unlocking.
- Creation of user stories and requirements documentation for relatives, care services, and administrators.
- Design of trust and quality assurance mechanisms with document upload, admin review process, and rating system.
- Coordination with stakeholders and validation of product decisions with potential users.
- Technical implementation:
- Design and implementation of the entire platform architecture as a solo developer.
- Design and implementation of a REST API with Spring Boot and Kotlin, including JWT-based authentication.
- Development of the frontend as a single-page application with Angular 17.
- Implementation of the AWS infrastructure with EC2, RDS PostgreSQL, S3, CloudFront, and IAM.
- Document upload with AWS S3 via presigned URLs for verification of care services.
- Email notifications via Resend API.
- AI-supported care service search via OpenAI API.
- Implementation of complete user flows such as registration, login, password reset, and placement process.
- Building an admin panel for user and care service management as well as analytics.
- CI/CD with GitHub Actions and containerized deployments with Docker.
- End-to-end tests with Playwright.
Technologies: Kotlin, Spring Boot 3, Spring Security, JWT, JPA/Hibernate, PostgreSQL, Angular 17, TypeScript, RxJS, AWS (EC2, ECS, S3, CloudFront CDN, RDS PostgreSQL, IAM), nginx, GitHub Actions, Playwright, Maven, Git, OpenAI API, Resend API, Docker, Scrum, i18n (DE/EN/TR), Kiro, feature-flag architecture.
Emmanuel Lampe
Last position:
Founder and sole developer
- Development of a SaaS platform for esports teams with roles, scheduling, statistics, and billing
- Planning and implementation of the architecture, external API integrations, and operations
- Stack: Laravel 13, React 19, TypeScript, PostgreSQL, Redis, and Stripe
Will Orrantia
Last position:
Solution Architect at Stuttgart Police Authority
Designing the migration strategy for WLS applications to the BKA cloud and Stack IT
Creating a hybrid cloud for internal testing and development with Kubernetes
Transforming the IT landscape from a legacy monolithic architecture to a cloud-based architecture
Integrating new CI/CD processes using Azure Pipelines
Quadrupled the throughput of personnel security checks
Migrated personnel security clearance applications to Docker-based applications
Built CI/deploy pipelines with Azure DevOps
Environment: Java Spring Boot, Kubernetes, Oracle WebLogic, OpenID, Camunda, JUnit, TOGAF
Albert Frischmann
Last position:
Lead Product Owner at CMBlu Energy AG
- Lead Product Owner for 4 development teams
- Leading and coordinating a greenfield project with parallel implementation of core components by independent teams; managing dependencies and resources
- Establishing a data lakehouse approach, including analysis of data volumes and future requirements as part of a cloud migration (best-of-breed approach)
- Responsible for requirements analysis, selection, and piloting of a LIMS/ELN system, supported by advising decision-makers and managing external vendors
- Introducing and managing an OpenWeb UI and Azure OpenAI-based RAG system to support knowledge extraction and data-driven analyses
- Setting up, configuring, and managing Jira projects, as well as developing project-specific workflows and automations
- Implementing classic Scrum processes with all ceremonies and taking on the Scrum Master role for all involved teams
- Assisting in hiring through interviews and assessments from a product owner's perspective
- Making key architectural decisions, including selecting the platform for the data lakehouse (Databricks) and the strategic integration of LIMS and analytics platforms
Achille Chimi
Last position:
Backend/Frontend Developer at ITZ-Bund
Development of a microservice application for calculating postings on accounts
Development of backend components with Java or JEE, Quarkus, Kafka, Rest API
Development of the test component with mocking frameworks (Mockito)
Development of integration test components
Creation of OpenAPI specification format
Configuration of CI/CD pipeline
Development of frontend components with React
Design, further development and optimization of system structures
Code review
Java Corretto 21, JEE, Quarkus, Golang
Reactive programming with Spring WebFlux, Project Reactor
Git, Azure DevOps for CI/CD pipeline, YAML, Json Swagger UI, Postman, Rest OpenAPI, Kafka Streams, Kafka Connect, Log4J
Microservices, Jira, Confluence, MySQL, Docker, Kubernetes (deployment via Helm charts)
Spring Security, OAuth 2, JWT, Sonarqube
IntelliJ, Maven, logging framework Splunk, Agile method Scrum, Nexus, Vaadin V24, build tool Vite
React, React.JS, Node.js, Jess/JavaScript, Tailwind CSS, Agile method Scrum, accessibility BITV, Playwright
Matthias Max
Last position:
Founder at CaseOS Low-Code Platform
Discover over 15,000 top freelancers
Statistics of experts using OpenAPI
Aggregated from the professional profiles of matched freelancers.
Experience
18 years (Germany: 19 years)
Position duration
2.7 years (Germany: 1.8 years)
Positions per freelancer
16 (Germany: 14)
Top business areas
Information Technology, Operations, Product Development
Top industries
Information Technology, Automotive, Government and Administration
Certification focus areas
Information Technology, Operations, Product Development
Bachelor's degree or higher
75% (Germany: 89%)
Master's degree or higher
50%
Certifications per freelancer
2
Most common languages
German, English, French
Speak two or more languages
100% (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 Stuttgart 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 Stuttgart 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 defines API contracts in a machine-readable format. Teams use it to describe endpoints, request and response bodies, auth schemes, and error handling before the first line of implementation. It keeps product, backend, and QA work aligned around one source of truth.
What it supports
- REST APIs and public partner APIs
- Mock servers and contract testing
- Client SDK generation
- Developer portals and documentation
Strong specialists know how to keep specs readable, versioned, and consistent across services.
Tooling stack
OpenAPI work often sits next to Swagger UI, Swagger Editor, Redoc, and code generators. It also connects with linting, schema validation, and CI checks so specs stay useful as APIs change. Good professionals can adapt the spec to the tools your team already uses.
When companies bring help
Companies usually need freelance OpenAPI expertise when an API initiative starts, when old documentation no longer matches the service, or when multiple teams need a shared contract. In Stuttgart, this often matters for industrial software, mobility systems, and platform teams that work across internal and external interfaces.
What strong specialists do
A strong OpenAPI professional writes clean definitions, catches edge cases early, and keeps naming and error models consistent. They understand JSON Schema, REST conventions, authentication flows, and versioning. They also know when to keep the spec simple instead of overengineering it.
Delivery and collaboration
OpenAPI specialists can work remotely or on-site, depending on how much workshop time and stakeholder review you need. For teams in Stuttgart, a short on-site kickoff can help align product, backend, and QA, while the detailed spec work is often done remotely. Clear review cycles matter more than location.
Frequently asked questions
The facts hiring teams ask for most often when it comes to OpenAPI.
OpenAPI is used to describe REST APIs in a structured, machine-readable way. It helps teams define endpoints, payloads, auth, and errors before implementation, so documentation, testing, and client generation stay in sync.
OpenAPI is the current specification name, while Swagger is the older umbrella name many teams still use. In practice, people may say Swagger UI or Swagger Editor when they mean the surrounding tooling, but the spec itself is OpenAPI.
A strong OpenAPI specialist is useful when an API needs a clean contract, existing docs no longer match the service, or multiple teams depend on the same interface. They are also valuable when you need mock servers, generated clients, or contract tests to reduce back-and-forth.
Good OpenAPI professionals usually also know REST design, JSON Schema, authentication patterns, versioning, and CI checks for spec quality. Many are comfortable with Swagger UI, Redoc, and code generation tools because the spec rarely lives on its own.
A simple documentation cleanup may only need a specialist who knows the spec well and can align it with existing endpoints. Larger API platforms need someone who can handle reusable components, governance, and review workflows across teams.
Yes, OpenAPI work is often well suited to remote collaboration because most of the work is spec writing, review, and testing. For teams in Stuttgart, an on-site kickoff can help with workshops and stakeholder alignment, but it is usually not required for the full engagement.
Look for OpenAPI files that are clear, consistent, and practical for real consumers. A strong specialist writes reusable components, accurate examples, and sensible error models, and they can explain trade-offs without hiding behind tooling.
OpenAPI is more than documentation because it can drive tests, mocks, SDKs, and validation. Plain docs explain an API; a good spec helps teams build and maintain it with fewer surprises.
The average hourly rate of freelancers in Stuttgart, Germany who have used OpenAPI in their recent projects is 97 €, which corresponds to a daily rate of about 774 € based on an 8-hour working day.
Of the freelancers in Stuttgart, Germany who have used OpenAPI in their recent projects, 75% hold at least a Bachelor's degree and 50% hold at least a Master's degree.
On average, freelancers in Stuttgart, Germany who have used OpenAPI in their recent projects have 18 years of professional experience, with a single engagement typically lasting around 2.7 years.
The most common languages among freelancers in Stuttgart, Germany who have used OpenAPI in their recent projects are German (100%), English (100%), and French (33%).
The most common industries among freelancers in Stuttgart, Germany who have used OpenAPI in their recent projects are Information Technology (100%), Automotive (67%), and Government and Administration (67%).
The most common business areas among freelancers in Stuttgart, Germany who have used OpenAPI in their recent projects are Information Technology (100%), Operations (100%), and Product Development (100%).
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.
Berlin 
Hamburg 
Munich 
Cologne 
Frankfurt Request a free demo
Get in touch with the FRATCH team and we will get back to you within 4 hours.
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We always have the time for a call or email!
Philipp Thomaschewski
FRATCH CEO
