OpenAPI Experts in Stuttgart
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Meet FRATCH Experts in Stuttgart, who have recently used OpenAPI
Sercan T.
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 placement platform that directly connects relatives of people in need of care 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 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 the sole 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 using presigned URLs to verify 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 the placement process.
- Development of 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.
Will O.
Last position:
Solution Architect at Polizei Behörde Stuttgart
Designed a migration strategy for WLS applications to BKA Cloud and Stack IT
Created a hybrid cloud for internal testing and development with Kubernetes
Transformed the IT landscape from an outdated monolithic architecture to a cloud-based architecture
Integrated new CI/CD processes using Azure Pipelines
Quadrupled the processing throughput for personnel security checks
Migrated personnel security screening applications to Docker-based applications
Implemented CI/deployment pipelines using Azure DevOps
Environment: Java Springboot, Kubernetes, Oracle Weblogic, OpenID, Camunda, JUnit, TOGAF
Emmanuel L.
Last position:
Founder and sole developer
- Development of a SaaS platform for esports teams with roles, planning, statistics and billing
- Design and implementation of the architecture, external API integrations and operations
- Stack: Laravel 13, React 19, TypeScript, PostgreSQL, Redis and Stripe
Albert F.
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 C.
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 M.
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% (Germany: 51%)
Certifications per freelancer
2
Most common languages
German, English, French
Speak two or more languages
100% (Germany: 94%)
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 Stuttgart 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 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 29 Oct 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%)
- Automotive (67%)
- Government and Administration (67%)
- Agriculture (50%)
- Banking and Finance (50%)
- Healthcare (50%)
- Insurance (50%)
- Transportation (50%)
Please note that freelancers can work across multiple industries, so percentages overlap.
About the technology
API contracts
OpenAPI is a machine-readable specification for describing HTTP APIs. It defines paths, parameters, request bodies, responses, authentication and reusable schemas in YAML or JSON. Teams use these contracts to align services, web applications and external consumers before implementation begins.
Practical use cases
OpenAPI supports both new API products and existing service estates. Strong specialists turn business requirements into clear, testable contracts and keep them useful throughout delivery.
- Define REST endpoints and reusable data models
- Document authentication, errors and response behaviour
- Generate client libraries, server stubs and reference pages
- Validate requests and responses in automated pipelines
Ecosystem and tooling
The specification works with tools including Swagger UI, Swagger Editor and OpenAPI Generator. Professionals may also use Redoc, Stoplight, Postman, contract-testing frameworks and CI pipelines. They understand version differences, extensions, JSON Schema compatibility and the trade-offs between generated and hand-written code.
When expertise matters
Companies often bring in freelance OpenAPI expertise when several teams need one dependable API contract, when documentation has fallen behind production, or when a public API must be made easier to consume. The work can include assessing an existing description, introducing governance, or preparing a migration from a proprietary format such as Swagger 2.0.
In Stuttgart, this can support industrial, mobility, software and enterprise teams working across internal sites and distributed delivery groups. A specialist should be comfortable with remote collaboration and, where needed, clear communication in English or German.
What strong specialists deliver
Quality is more than valid YAML. Experienced professionals model resources consistently, distinguish required from optional data, describe failure cases and avoid ambiguous terms. They connect the contract to security controls, observability, automated tests and release processes.
- Review naming, schemas, pagination and error conventions
- Check that documentation reflects real behaviour
- Establish rules for compatibility and versioning
- Explain decisions to product, security and delivery teams
Choosing the right professional
Look for evidence of API lifecycle work, not only familiarity with Swagger UI. Ask how the specialist handles breaking changes, reusable components, authentication schemes and differences between an API description and an implementation. A practical review of one representative endpoint can reveal precision, communication style and attention to consumer needs.
Frequently asked questions
The facts hiring teams ask for most often when it comes to OpenAPI.
OpenAPI describes how an HTTP API behaves, including endpoints, inputs, outputs, authentication and errors. Companies use it to create shared contracts, publish documentation, validate traffic and generate client or server code.
OpenAPI is the open specification maintained by the OpenAPI Initiative, while Swagger is the earlier name and a family of tools associated with it. Swagger 2.0 was succeeded by OpenAPI 3.x, so a professional should identify the document version and tool compatibility before changing an API.
OpenAPI work benefits from knowledge of REST design, HTTP semantics, JSON Schema, OAuth 2.0, API gateways and automated testing. Experience with Git, CI pipelines, service integration and documentation tools is also valuable.
OpenAPI experience should match the project’s risk and scope rather than a fixed duration. A simple internal service may need contract design and documentation skills, while a public or regulated API calls for versioning, security, compatibility and governance expertise.
OpenAPI projects are often well suited to remote collaboration because contracts, reviews and generated documentation are shared digitally. Stuttgart-based teams should agree on workshop times, repository practices and whether communication is expected mainly in English, German or both.
OpenAPI is designed primarily for HTTP APIs, especially REST-style services. It is not a complete native description format for GraphQL schemas or asynchronous event contracts, where technologies such as GraphQL SDL or AsyncAPI may be more appropriate.
OpenAPI quality can be assessed by checking whether examples, schemas, status codes and security requirements match real service behaviour. Reviewers should also test validation, inspect breaking-change handling and ask consumers whether the documentation supports implementation without guesswork.
OpenAPI specialists should clarify the source of truth, target specification version, existing tooling, API ownership and release process. They should also ask whether the deliverable is a new contract, a reverse-engineered description, generated artifacts, governance rules or a complete documentation workflow.
The average hourly rate of freelancers in Stuttgart, Germany who have used OpenAPI in their recent projects is 96 €, which corresponds to a daily rate of about 771 € 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 
Dusseldorf Countries:
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