OpenAPI Experts in Hamburg
for reliable APIs, matched in minutes with vetted and available freelancersHire experts who design clear API contracts, generate documentation and client libraries, and integrate OpenAPI with REST services, gateways and CI/CD workflows. FRATCH connects you with vetted, available freelancers through fast, precise AI matching.
Meet FRATCH Experts in Hamburg, who have recently used OpenAPI
Daniel S.
Last position:
Senior Software Engineer at energielenker solutions GmbH
- Designed and implemented a Python-based ETL pipeline with the Dagster framework to transform raw energy data from heterogeneous sources using InfluxDB and visualizations in Grafana
- Defined time-based and dependency-based jobs
- Deployed to managed Kubernetes clusters using Helm
- Integrated InfluxDB Cloud
- Prepared data for use in Grafana, including cleaning, normalization, and time-based resampling in Python
- Developed dashboards and visualizations in Grafana
- Developed unit tests with mocking using pytest
- Set up a CI/CD pipeline in GitLab
Technologies: Python, Dagster, InfluxDB, Grafana, pandas, pytest, REST, CI/CD, GitLab, Container, Kubernetes, Helm, Docker, Cloud
Rutger B.
Last position:
Partner & Managing Director at AI.IMPACT
- Building an AI & Data Consultancy Practice with the goal of helping European companies adopt Artificial Intelligence and modern data platforms
- End-to-end further development of a production system using modified coding agents (OpenCode). Tech stack: Kubernetes, Argo, Keycloak, Typescript, Grafana, GitOps, DevOps, Playwright
- Internal research project on the use of coding agents in the field of mathematical logic for creating formal models. Use of Cursor IDE and Codex, Codex CLI. Architecture design, quality control and refactoring, as well as writing code and tests. Repository (open source) available pre-launch
- Research on the role of mathematical logic as a formal language that connects IT and AI with business processes
- Project lead for collecting and deploying parking recommendations for rail vehicles with significant savings potential based on real-time data in a mobility and transport company
- Project lead for collecting and distributing process measurement points for real-time control in a mobility and transport company
- Deputy application owner for an app used for communication in the dispatching and provision of rail vehicles
Rizwan B.
Last position:
Software Developer/Database/Devops at Sutor Bank
Project:
- Migration of existing VB6 applications to C# (Web API, web app)
- Report development and risk management systems (C#, API interfaces, databases)
- Document archive (API interfaces, databases)
Team size: 9 people
- Reports for Risk and Credit Management Development and maintenance of report structures to support risk and credit decisions, including data modeling, validation, and automated delivery for business departments.
- Migration and maintenance of a legacy system to the latest version of .NET for the asset management system Planning and execution of the modernization of an existing asset management system, including code refactoring, performance optimization, test automation, and sustainable maintenance after migration.
- Replacement of the COM-based archive connection with a REST API Redevelopment of the connection of the document archive (HYPARCHIV) to a REST API based on OpenAPI/Swagger, including archiving with index and stamp fields as well as PDF export into the customer portal.
- Redesign of payment receipt processing Replacement of an existing Oracle PL/SQL process with a new implementation in C# based on a business concept, including business alignment, data modeling, and test coverage.
- Design and implementation of tests, creation of deployment pipelines, and documentation
- Further development and implementation of change requests.
- Regular code reviews within the team as well as optimization of application scalability and stability
Technologies: C#, .NET 10, ASP.NET, Unit of Work, IoC, Three-Tier Architecture, Entity Framework Core, DB First, Web API, Swagger, OpenAPI, Python, Oracle, HYPARCHIV, Azure, PowerBI, DevOps, AKS (Azure Kubernetes Service), GIT, xUnit, NSubstitute, TypeScript, Vue.js, Pinia,
Methods: agile development using Scrum
Florian W.
Last position:
Software Engineer at micimo GmbH
- Developing a professional scheduler for organizations with specific detailed requirements
- Evaluating different existing software solutions
- Creating a list of technical requirements
- Implementing these requirements
- Selected technologies: WebDAV, CalDAV, Rust, Baikal, OAuth, Keycloak
Rainer D.
Last position:
Enterprise Architecture Management / Backend Software Developer at Polizei Hamburg
- Several projects in a police context
- Model and document police procedures/projects with Archimate (as-is/to-be) in the context of P20 (BKA)
- Create software architectures with microservices
- POC development with Springboot/Docker/Kubernetes
- Project size: 10 people
- Enterprise architecture management with Togaf and Archimate
- Backend software development Springboot
- DevOps with Kubernetes
- Implemented using: Java 17/21, Springboot 3, P20 architecture, Togaf, Archimate
Patrick V.
Last position:
Senior Director, Retail Media at EUROBAUSTOFF Handelsgesellschaft mbH & Co. KG
- Strategic consulting on marketing funds (WKZ) and retail media, focusing on monetization opportunities and data-driven business models
- Conducting a portfolio analysis of existing WKZ measures to assess the revenue and ROI impact of WKZ investments on supplier performance
- Potential analysis of digital WKZ products and initiatives to identify growth and efficiency levers
- Preparing and presenting the results to management and deriving a strategic move-forward plan
- Designing and facilitating several executive workshops to develop a holistic retail media vision and transformation roadmap
- Defining and prioritizing retail media business cases for data-driven evaluation of investment options
- Developing a technical target architecture considering heterogeneous ERP infrastructures and designing an integrated loyalty program
- Designing change management, including impact analysis on organizational structures and processes
- Creating and presenting C-level decision templates
- Establishing a clear retail media governance structure and technical foundation for data-driven marketing
- Developing a roadmap for implementation in 2026
Bastian I.
Last position:
Senior Backend Engineer Go & Technical Consultant at Regulated trading system for digital assets
- Technical consulting to meet regulatory MiCA requirements for a digital trading platform
- Design and development of backend components and APIs to comply with transparency and auditability requirements
- Optimization of core functions in order execution and market data delivery with a focus on performance and reliability under high load
- Conducting job interviews and structured onboarding of new developers
- Successful and timely implementation of the regulatory MiCA requirements, ensuring uninterrupted operations
- Reduction of user issues and common support requests by fixing complex backend problems
- Strengthening the development team through effective onboarding, mentoring, and knowledge sharing
Jonas T.
Last position:
IT Consultant at Bechtle AG
- Prequalified 200 demands within five weeks on the multi-cloud-commerce platform bechtle-clouds.com with three external consultants
- Served a dual role as project manager and requirements engineer for various enhancements
- Domain topics: reimplementation of Entra ID Sync, improvement of support processes, optimizations in the product catalog
- Demand and project management in ServiceNow
- Refinement of epics and stories with internal teams and external service providers
- Management of the external international service provider
Daniel Y.
Last position:
Senior Frontend Developer at node.energy
- Significant enhancement of the B2B React SPA software "opti.node" for commercial operations management for renewable energy plant operators
- Introduced features not previously available on the market, resulting in a significant revenue increase
- Comprehensive automated tests within Storybook
- Introduced a UI library to improve developer experience and speed up feature development by about 40%
- Clear presentation of complex commercial and legal issues, with intuitive UX and UI
- UX consulting to shorten essential interaction flows by 75%
Marcel S.
Last position:
Lead Developer / Software Architect at Rezeptprüfstelle Duderstadt GmbH
Responsible for the new development of billing and auditing software for prescriptions (prescriptions) to fully check and evaluate e-prescriptions for correctness (content, billing)
The system consists of several contexts that run as services (Docker containers):
Checking and processing data deliveries via FTP and email
Managing invoices, clearings, advance payments and deductions
Managing and running audit rules and audit folders
Evaluations based on Metabase
Developer Stack: Kotlin, Vue 3 / Vuetify 3, ANTLR, Spring Boot 3, REST API, Gradle, Docker, GitLab, PostgreSQL, Kafka, Keycloak, Scrum, Grafana, Loki, Testcontainers, Prometheus
Florian F.
Last position:
Solution Architect with Developer Focus at SymFinIT Solutions GmbH
- Further development of a finance layer for subscription and one-time purchase billing and accounting.
- Technologies: Kotlin, AWS (SQS, S3, ElastiCache, Aurora), React, TypeScript, Coroutines, IntelliJ IDEA, Spring (Boot, Data, WebFlux), JUnit, Testcontainers, Cucumber, Liquibase, PostgreSQL, Webservices (REST), R2DBC, OpenAPI 3, Gradle, GIT, Docker, Netty, GitHub Actions, Jira/Confluence, arc42
Jürgen B.
Last position:
Software Developer at Inform AG
- Coaching junior developers
- Further development and customer-specific extensions of a standard software product (microservices (DDD) and partly monolith)
- Interface extensions
- Web services
- Test automation
- Design
- Technologies used: Java8, Java17, TypeScript, Python, PostgreSQL, Spring (Integration, Data, Boot), JPA, AWS (Cloud, Lambda, EC2, SQS/SNS), Microservices, Fitnesse/Cucumber, Gitlab
Andreas S.
Last position:
Lead Developer at Software
- Extended the document management system with a standard CMIS (Content Management Interoperability Services) interface
- Implemented CMIS core services like navigation, access rights, search, CRUD operations, and versioning in Java
- Implemented based on RESTful / OpenAPI services
- Delivered as a fat-jar and native container image
- Deployed on-premises and serverlessly as an Azure Container Application using Terraform
- Improved team autonomy through infrastructure engineering and short feedback loops
- Established observability with OpenTelemetry, Azure Monitor, and Azure Logic Apps
- Introduced Terraform and trunk-based development processes
- Ensured quality with BDD tests in C# using SpecFlow and Testcontainers
- Created Azure DevOps pipeline integration tests
- Introduced cloud deployment processes
- Trained staff in cloud and Terraform
Mark P.
Last position:
Full-Stack Software Developer, Product Data Import at Otto (GmbH & Co KG)
- Manage and operate the product data import services for the Otto merchant
- Enhance and maintain the backend systems
- Optimize and maintain AWS infrastructure
- Build a new product data import API
- Design and plan stories and features
- Conduct code reviews to ensure code quality and best practices
- Analyze and fix bugs
- Technologies: Java, Spring Boot, Kafka, AWS, Fargate, Terraform, MongoDB, Mongo Atlas, OpenAPI, GitHub, GitHub Actions, GitHub Copilot, Akhq, Debezium, JUnit, Test Containers, Hexagonal Architecture
René S.
Last position:
CRM Developer at CiS GmbH
- Developed a greenfield CRM for managing incoming customer requests for a municipal utility provider
- Implemented with PHP/Symfony 5, EasyAdmin, Doctrine ORM and Oracle XE
- Handed over to CiS GmbH after initial groundwork as planned
Discover over 15,000 top freelancers
Statistics of experts using OpenAPI
Aggregated from the professional profiles of matched freelancers.
Experience
19 years
Position duration
1.6 years (Germany: 1.8 years)
Positions per freelancer
12 (Germany: 14)
Top business areas
Information Technology, Product Development, Quality Assurance
Top industries
Information Technology, Banking and Finance, Retail
Certification focus areas
Information Technology, Product Development, Project Management
Bachelor's degree or higher
91% (Germany: 89%)
Master's degree or higher
45% (Germany: 50%)
Doctorate
18% (Germany: 11%)
Certifications per freelancer
2
Most common languages
German, English, French
Speak two or more languages
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 Hamburg 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 Hamburg 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 (60%)
- Retail (53%)
- Transportation (47%)
- Healthcare (40%)
- Automotive (33%)
- Energy (33%)
- Insurance (33%)
Please note that freelancers can work across multiple industries, so percentages overlap.
About the technology
API contracts
OpenAPI is a vendor-neutral specification for describing HTTP APIs in a structured, machine-readable format. It defines paths, parameters, request bodies, responses, authentication and reusable schemas, giving product, frontend and backend teams a shared contract before and during implementation.
What it enables
OpenAPI supports the delivery of:
- REST API design for web and mobile products
- Interactive reference documentation for internal and external consumers
- Generated client libraries, server stubs and validation rules
- Contract testing and consistent API governance
Ecosystem and tooling
Professionals work with the OpenAPI Specification alongside Swagger UI, Swagger Editor and Swagger Codegen or OpenAPI Generator. They also use tools such as Postman, Stoplight, Redoc, API gateways and schema validators. Strong practice includes version control, linting, reusable components and integration with CI/CD pipelines.
When expertise matters
Companies bring in freelance expertise when an API landscape is growing inconsistent, a platform is being opened to partners, or documentation no longer matches production behavior. In Hamburg, this can support logistics, commerce, media and industrial companies working across distributed product teams. Specialists can also establish a practical contract between local stakeholders and remote delivery teams.
Typical project work
An OpenAPI specialist may contribute to:
- Auditing existing specifications against live endpoints
- Designing resource models, error formats and authentication flows
- Migrating Swagger 2.0 documents to current OpenAPI versions
- Connecting specifications with gateways, tests and release pipelines
- Creating documentation that external consumers can use without hand-holding
Signs of strong practice
A capable professional treats the specification as part of the product, not as an afterthought. They clarify ambiguous behavior, model edge cases, keep examples executable and explain trade-offs between generated and hand-written code. They also understand HTTP semantics, security schemes, backward compatibility and the operational limits of the services behind the contract.
Frequently asked questions
What clients ask us most about OpenAPI — answered in short.
OpenAPI is used to describe HTTP APIs so teams and tools share a precise contract. It supports documentation, client generation, server scaffolding, validation, testing and governance across the API lifecycle.
OpenAPI is the specification now maintained as an open standard, while Swagger is the name associated with the earlier specification and a family of tools. Many teams still use Swagger UI or Swagger Editor with an OpenAPI document.
A strong OpenAPI freelancer should understand HTTP, REST design, JSON Schema, authentication and API security. Experience with tools such as OpenAPI Generator, Swagger UI, Postman, API gateways and CI/CD automation is also useful.
The right level depends on the work. A focused documentation update may need solid specification and API knowledge, while a platform-wide contract or migration calls for a professional who can handle governance, compatibility, tooling and coordination with service teams.
Yes. OpenAPI artifacts are text-based and work well with version control, pull requests and remote reviews. On-site sessions in Hamburg can still help when teams need to agree on domain models, ownership or API standards.
Review whether the OpenAPI document matches real behavior, covers errors and security, uses consistent reusable schemas and gives consumers enough working examples. Ask the professional to show how the specification is validated and kept in sync through delivery.
OpenAPI records design decisions, but it does not make those decisions for a team. Professionals still need to define resource boundaries, naming, error behavior, lifecycle rules and compatibility expectations with product and service owners.
Yes. An OpenAPI specialist can document current endpoints, identify inconsistencies, introduce reusable components and add validation or contract tests without changing the underlying services. They can then plan improvements that preserve compatibility for existing consumers.
The average hourly rate of freelancers in Hamburg, Germany who have used OpenAPI in their recent projects is 102 €, which corresponds to a daily rate of about 818 € based on an 8-hour working day.
Of the freelancers in Hamburg, Germany who have used OpenAPI in their recent projects, 91% hold at least a Bachelor's degree, 45% hold at least a Master's degree, and 18% hold a doctorate.
On average, freelancers in Hamburg, Germany who have used OpenAPI in their recent projects have 19 years of professional experience, with a single engagement typically lasting around 1.6 years.
The most common languages among freelancers in Hamburg, Germany who have used OpenAPI in their recent projects are German (100%), English (93%), and French (13%).
The most common industries among freelancers in Hamburg, Germany who have used OpenAPI in their recent projects are Information Technology (100%), Banking and Finance (60%), and Retail (53%).
The most common business areas among freelancers in Hamburg, Germany who have used OpenAPI in their recent projects are Information Technology (100%), Product Development (100%), and Quality Assurance (87%).
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.
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