Kotlin Experts in Cologne
, matched in minutes from over 15,000 CVsHire experts who create Android apps, backend services with Kotlin and Spring Boot, and multiplatform products with Kotlin Multiplatform. FRATCH matches you quickly and precisely with vetted, available freelancers.
Meet FRATCH Experts in Cologne, who have recently used Kotlin
Marc S.
Last position:
Fullstack Developer at PLANT-MY-TREE
PLANT-MY-TREE®-per-order
The application enables Shopify merchants to automatically place tree-planting orders for every incoming order. By integrating ecological contributions directly into the purchase process, the manual effort for tracking and billing reforestation initiatives is eliminated. The system increases transparency for end customers through real-time visualizations of the ecological impact directly in the storefront. The architecture is based on a modular monolith with Spring Boot in the backend and an integrated React app inside the Shopify admin area. The solution uses webhooks to capture order data in an event-driven way and integrates the weclapp ERP system for automated monthly invoicing. An app proxy mechanism provides dynamic statistics such as CO2 compensation and planted trees without any performance loss for the merchant shop.
Tasks:
- Design of the modular software architecture based on Spring Modulith to ensure high maintainability
- Development of the event-driven business logic for evaluating Shopify orders via webhooks
- Implementation of automated invoicing by connecting the weclapp REST API
- Building the frontend using React Router and Shopify App Bridge for native integration
- Design of the database model and implementation of the persistence layer with JPA/Hibernate and Prisma
- Integration of internationalization processes for global use in the frontend and email communication
- Automation of deployment processes using Docker and GitLab CI/CD
Project skills: Java 25, Spring Boot, Spring Security, Spring Modulith, Hibernate, JPA, REST API, PostgreSQL, Maven, Liquibase, React, TypeScript, React Router, Vite, Node.js, Prisma, Zod, Docker, Docker Compose, GitLab CI/CD, Shopify CLI, Shopify App Bridge, Polaris, weclapp, i18next, Lombok, Vitest
Thomas P.
Last position:
Freelance Software Architect at Self-employed
Ayhan G.
Last position:
Senior QA Engineer / Test Automation Engineer / SDET at Rewe digital
Consulting, designing, and implementing the software testing lifecycle for multiple Android apps and backends Introducing test automation with Appium, SpringBootTest, RestAssured Setting up and managing emulators Developing an E2E library, an integration library, a Testcontainers library, and other libraries Developing, implementing, and advising on CI strategies Building the test environment with Testcontainers and virtualization Developing and implementing test cases for integration tests and end-to-end tests Establishing a maintainable test architecture with low entry barriers to simplify the creation of automated tests Some tools and technologies used: JUnit, RestAssured, Testcontainers, Kubedock, Appium, Android emulator, Jira Xray, Mockito, WireMock, Spring Framework, Kotlin
Andreas E.
Last position:
Consultant at Iteratec GmbH
Predrag P.
Last position:
Test Developer | Test Automator at CreditReform
Technologies: Java 25, Selenium, Insomnia, SSO, GitLab, Jenkins, Docker, Kubernetes, Jira, IntelliJ, Nexus, Oracle, MariaDB, Spring Boot, Grafana, Concept Board, Vue.js, OpenAPI, Kotlin. Implementation, maintenance, and extension of automated end-to-end regression tests for UI and API interfaces. Appropriate and targeted test automation across multiple software products, including Java-based Windows applications. Automating business processes with Selenium, reset jobs, and DB import jobs, as well as creating test concepts, test case descriptions, and structured bug reporting.
Louis N.
Last position:
Specialist in Adobe Experience Manager & Microservices at Nguenkam Consulting & Engineering
Java 11/21
Springboot
Swagger/OpenApi
Azure Pipelines
Trivy Integration
Apache Sling
OSGI
Java Content Repository (JCR)
Apache Jackrabbit Oak
Adobe HTL
GraphQL
Maven
GitLab
IntelliJ
Azure Cloud
Azure DevOps
Terraform
AEM specialist in the Scrum team
Development and deployment of microservices via Open API interfaces
Operation of microservices in the Azure Cloud
Implementation of AEM modules and integration with microservices
Member of the knowledge transfer team and a backend coordination team
Sebastian T.
Last position:
Software Engineer / Cloud Engineer at OC Fulfillment GmbH
- Hybrid role as the first software engineer in the company to bootstrap the organization, laying out technical foundation and advising management on organizational aspects.
- Set up the SaaS platform architecture, selected languages and tools, and designed processes to deliver customer value quickly and reliably.
- Designed and implemented build and continuous deployment pipeline with multi-tenant approach enabling extreme scaling of the SaaS platform.
- Established initial ITSM and support processes, provided monitoring and alarming, and participated in the on-call team.
- Proposed new approaches to scale the platform and improve backend interfaces to mitigate bugs and communication overhead.
- Mentored new employees and served as a trustful team member and lateral leader.
- Conducted interviews for technical roles.
- Used technologies: Typescript, Node.js, Bash, Google Cloud Platform (App Engine, Cloud Run, Cloud Functions, Google Endpoints, Firebase), GitHub Actions, Docker, Terraform, MongoDB, Firebase, REST APIs, GraphQL.
Jacqueline H.
Last position:
Kitchen Appliance Manufacturer
Setting up and enhancing an international subscription management system
Migrating and decommissioning a Hybris-SAP system and integrating Zuora
Implementing numerous interfaces to various systems (external and internal)
Setting up and improving monitoring with Grafana, Prometheus, and Databricks
Introducing logging with Loki
Implementing business requirements using jQuery, Thymeleaf, Spring Boot, Java, Go, and Python
Adjusting and extending the GitLab CI pipelines
Setting up and extending infrastructure as code with Terraform and ArgoCD on AWS
Setting up and running E2E and performance tests
Expanding the Databricks business intelligence solution to provide various KPIs
Responsibilities: Architecture, DevOps, development, unit tests, coaching employees and apprentices, E2E, smoke, and integration tests, agile methods consulting (Kanban, Scrum)
Technologies and methods: Java, Go, Kotlin, Node.js, Spring Boot, SOAP/REST, Quarkus, Thymeleaf, Vaadin, Slack, Jira, Confluence, IntelliJ, GitLab, SQS, Kafka, AWS, Kubernetes, Terraform, Maven, Gradle, GitLab CI, Databricks
Andreas B.
Last position:
Senior Frontend Developer at Roadex
- Development of an app
- Technologies: React Native, Expo, SupaBase, TypeScript, GitHub, Trello
Alexander J.
Last position:
Freelancer at Bayer
- IoT development in Kotlin/Python.
Jacqueline K.
Last position:
OTTO
- Design, development, and monitoring of microservices
- Migrating functions from a monolithic system into separate microservices
- Designing and implementing new microservices (backend and frontend)
- Setting up and maintaining a CI/CD pipeline (GitHub Actions)
- Configuring cloud infrastructure with AWS CDK and Terraform
- Designing and implementing event-driven communication with AWS SNS/SQS and Apache Kafka
- Ensuring code quality through Test Driven Development (TDD), static code analysis, and Clean Code
Discover over 15,000 top freelancers
Statistics of experts using Kotlin
Aggregated from the professional profiles of matched freelancers.
Experience
18 years (Germany: 17 years)
Position duration
2.2 years (Germany: 2.7 years)
Positions per freelancer
9 (Germany: 12)
Top business areas
Information Technology, Product Development, Quality Assurance
Top industries
Information Technology, Retail, Transportation
Certification focus areas
Information Technology, Product Development, Project Management
Bachelor's degree or higher
100% (Germany: 93%)
Master's degree or higher
75% (Germany: 56%)
Doctorate
13% (Germany: 9%)
Certifications per freelancer
2
Most common languages
German, English, French
Speak two or more languages
100% (Germany: 98%)
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 Cologne 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 Cologne using Kotlin
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.
Kotlin 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 (91%)
- Retail (55%)
- Transportation (45%)
- Healthcare (36%)
- Banking and Finance (27%)
- Insurance (27%)
- Telecommunication (27%)
- Manufacturing (18%)
Please note that freelancers can work across multiple industries, so percentages overlap.
About the technology
Kotlin at a glance
Kotlin is a statically typed programming language from JetBrains. It runs on the Java Virtual Machine, interoperates closely with Java, and also targets JavaScript and native platforms. Companies use it for Android applications, backend services, shared mobile code, automation and data-focused tools.
Where Kotlin fits
Kotlin combines concise syntax with null-safety, extension functions, coroutines and strong tooling. Its compatibility with Java lets teams modernize existing systems without replacing the whole codebase. Kotlin Multiplatform can share business logic across Android, iOS, desktop and web applications while keeping platform-specific interfaces where needed.
Common project work
- Android apps with Jetpack Compose, Android SDK and lifecycle components
- REST and event-driven services with Spring Boot, Ktor or Micronaut
- Shared domain logic with Kotlin Multiplatform and Compose Multiplatform
- Java-to-Kotlin migrations, API refactoring and test automation
- Integrations with databases, messaging systems and cloud services
Ecosystem and tooling
Kotlin specialists commonly work with Gradle, IntelliJ IDEA, Android Studio, Kotlin DSL and static analysis tools such as Detekt and Ktlint. They may also use Spring Boot, Ktor, Exposed, Hibernate, Coroutines, Flow and serialization libraries. Strong work includes automated tests with JUnit, MockK or Kotest, plus dependable CI pipelines and observability.
When companies need support
Freelance expertise helps when an Android product needs a new release, a Java service is being modernized, or a team is evaluating shared code across mobile platforms. It is also useful for short delivery phases, architecture reviews and specialist cover during hiring gaps. In Cologne, remote collaboration can work well when repositories, decisions and reviews are kept transparent; on-site work may suit teams with close product and hardware coordination.
What strong specialists deliver
The best Kotlin professionals understand more than language syntax. They make sound choices about coroutine scopes, structured concurrency, API design, memory use and module boundaries. They explain trade-offs clearly, protect compatibility with Java and existing Android code, and leave behind readable tests, documentation and maintainable builds. For teams in Cologne, practical English or German communication can be agreed at the start.
Frequently asked questions
Before you brief your next project: the most common questions about Kotlin.
Kotlin is widely used for Android apps, backend APIs, server-side services and shared mobile logic. Teams also use it for desktop tools, browser-targeted code and integrations where Java compatibility is valuable.
A strong Kotlin specialist can add new services alongside Java and migrate code gradually. Kotlin offers null-safety, concise syntax and coroutines, while Java may remain preferable where a team depends heavily on existing libraries, conventions or specialist knowledge.
Kotlin is a natural fit for modern Android work and is supported throughout the Android ecosystem. Professionals may combine it with Jetpack Compose, Android SDK components, coroutines and lifecycle-aware architecture rather than treating the language alone as the complete solution.
A capable Kotlin freelancer may also understand Android architecture, Spring Boot or Ktor, SQL, REST and event-driven design. Testing, Gradle, CI pipelines, cloud services and observability are important when the work reaches production.
The right level depends on the work, not on a fixed number of years. Kotlin migration, concurrency, multiplatform architecture and production incidents call for a specialist who has handled comparable systems, while a contained feature may need a narrower skill set.
Yes. Kotlin work is well suited to remote collaboration when teams use clear tickets, shared repositories, code reviews and reliable release practices. Cologne companies should define overlap hours, documentation habits and whether English, German or both are needed.
Kotlin Multiplatform can make sense when mobile products should share domain logic, networking or data handling without forcing identical user interfaces. A specialist should first assess platform differences, team capability, build complexity and the long-term maintenance model.
Review how the Kotlin professional explains trade-offs around coroutines, nullability, testing and compatibility with Java. Ask for examples of maintainable production code, investigate their approach to failure handling and inspect whether delivery includes tests, documentation and a clean build process.
The average hourly rate of freelancers in Cologne, Germany who have used Kotlin in their recent projects is 93 €, which corresponds to a daily rate of about 744 € based on an 8-hour working day.
Of the freelancers in Cologne, Germany who have used Kotlin in their recent projects, 100% hold at least a Bachelor's degree, 75% hold at least a Master's degree, and 13% hold a doctorate.
On average, freelancers in Cologne, Germany who have used Kotlin in their recent projects have 18 years of professional experience, with a single engagement typically lasting around 2.2 years.
The most common languages among freelancers in Cologne, Germany who have used Kotlin in their recent projects are German (100%), English (100%), and French (18%).
The most common industries among freelancers in Cologne, Germany who have used Kotlin in their recent projects are Information Technology (91%), Retail (55%), and Transportation (45%).
The most common business areas among freelancers in Cologne, Germany who have used Kotlin in their recent projects are Information Technology (100%), Product Development (100%), and Quality Assurance (55%).
Main locations of FRATCH Experts, who have recently used Kotlin
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 Stuttgart Dusseldorf Leipzig Dortmund Essen Bremen Dresden Hanover Nuremberg 
Berlin 
Hamburg 
Munich 
Frankfurt 
Dusseldorf Countries:
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