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Sebastian Consulting
Sebastian Fastner
Sebastian FastnerDiplom-Informatiker (FH)

24 years of software development leave a mark – in my case, products running in more than ten countries. At DWS Group, I built an investment platform serving European and Asian markets. At Witt, I laid the technical foundation for 17 online shops. For Regrello, I developed an AI translation pipeline that enables users of different languages to collaborate seamlessly.

I'm at home in TypeScript and React. On top of that comes a tooling stack that shows frontend has long been more than just UI: Vite, Vitest, Playwright, Infrastructure as Code, CI/CD. But technology alone doesn't interest me much. What drives me: architectures that can grow without collapsing under their own weight. Code that the next team can understand too. And the honest assessment of when a new tool adds real value – and when it just adds complexity.

At Sebastian Software, I work as a Senior Technology Consultant at the intersection of frontend architecture, mobile, and internationalization. Not as an external contractor who delivers code, but as a partner who shares knowledge and helps teams grow.

Core Competencies

TypeScriptReactReact RouterVanilla ExtractConvexNode.jsCloud-InfrastrukturInfrastructure as CodeViteVitestPlaywrightCI/CDGraphQLTemporal

Personal Details

Location
Mainz, Germany
Work Model
preferably remote + occasional on-site
Languages
German and English
Citizenship
German
Contact
s.fastner@sebastian-software.de
Phone
+49 176 32042696

Industry Experience

10
Telecommunications
7
Fintech
3
E-Commerce
2
Enterprise Software

My Stack (Q1/2026)

Frontend

  • TypeScript
  • React
  • React Router
  • Vanilla Extract

Backend

  • Convex
  • Node.js
  • Cloud-Infrastruktur
  • Infrastructure as Code

Tools

  • Vite
  • Vitest
  • Playwright
  • CI/CD

Project Experience

Regrello
Regrello · San Francisco, USA
Senior Technology Consultant10/2024 – 09/2025

Regrello Corp. – an AI-focused startup in supply chain management, acquired by Salesforce in late 2025 – needed a complete internationalization effort leveraging large language models. I led this initiative and evaluated the quality of translations from English into six target languages: French, German, Chinese, Spanish, Korean, and Thai. The developed plugin system enables automatic translation of all user inputs, significantly simplifying the product's international scaling.

A plugin system for the Go backend's GraphQL resolvers and mutations formed the core of the solution. New user inputs are automatically translated via LLM (Google Gemini and gemma3) and cached in Redis. Translations are orchestrated through Temporal workflows, for which I implemented corresponding queues and workers in Go. Since plaintext user content could not be stored in the Temporal queue for security reasons, I developed a performant encryption system for Temporal. The backend was structurally improved and decoupled, making it more maintainable and comprehensible.

GoGraphQLRedisTemporalGoogle GeminiTypeScriptNode.js
DWS / MorgenFund
DWS / MorgenFund · Frankfurt am Main, Germany
Senior Frontend Architect10/2020 – 07/2024

As Senior Frontend Architect, I led the ongoing development of the DWS Robo-Advisor WISE, which from 2022 was continued under the spin-off MorgenFund GmbH. The migration to a cloud system modernized the infrastructure and enabled more flexible scaling. Porting the dashboard from React to React Native opened mobile devices as an additional channel for retail investors. The successful rollout to further European and Asian markets demonstrated the platform's international scalability.

Azure served as the new cloud platform for the system. Implementing a continuous deployment strategy accelerated release cycles and increased deployment reliability. The React Native port enabled code sharing between web and mobile. The multi-market architecture supported varying regulatory requirements and localizations.

ReactReact NativeTypeScriptAzureContinuous DeploymentNode.js
Witt-Gruppe (Otto Group)
Witt-Gruppe (Otto Group) · Weiden in der Oberpfalz, Germany
Senior Frontend Architect04/2019 – 09/2020

17 online shops of the Witt Group – a subsidiary of the Otto Group – were to be replaced by a complete redevelopment. I led this initiative with a focus on scalability, multi-brand support across international markets, and ease of maintenance. The integration of Contentful empowered the SEO team with dynamic pages and customizable elements on the shop pages. The new architecture enabled faster time-to-market for new brands and markets.

Next.js, React, and Styled Components formed the frontend foundation, with product data connected to the ABOUT YOU backbone. Apollo GraphQL encapsulated the backend systems, creating a unified API layer. The deployment infrastructure with Kubernetes and Vault on AWS enabled secure continuous deployment. An automated test infrastructure with GraphQL query tests ensured release quality.

Next.jsReactApollo GraphQLContentfulAWSKubernetesNode.js
DWS (Deutsche Bank)
DWS (Deutsche Bank) · Frankfurt am Main, Germany
Senior Frontend Architect04/2016 – 03/2019

As Senior Frontend Architect, I developed a white-label investment platform (WISE) for DWS – from prototype phase to production system. The prototype served as a sales pitch for internal funding and presented a wizard for surveying end customers about their investment profile. The complete platform – comprising risk profiling, onboarding with digital contract signing via DocuSign, and a dashboard – was rolled out to multiple European and Asian countries.

Vue.js and MobX initially formed the basis of the prototype; after cross-project alignment, the frontend was ported to React and TypeScript. I created an enterprise-wide UI component library based on React and was responsible for the complete tooling stack with Webpack, Babel, and ESLint. Spring Boot served as middleware to the production investment and CRM systems, while Keycloak with OpenID/OAuth handled identity management.

ReactTypeScriptVue.jsSpring BootKeycloakDocuSignNode.js

Additional Projects

Deutsche TelekomJako-oSuzuki DeutschlandDeutsche Bank3ado AGnetz98CommerzbankTechnische Hochschule Bingen
PeriodClientRoleTechnologies
2016Deutsche TelekomSenior Application ArchitectAngularJS, HTML5, PhoneGap, and OAuth2
2015–2016Jako-oLead Application ArchitectJavaScript, SPA, REST API, and Mobile-Optimierung
2015Deutsche TelekomLead Application ArchitectPhoneGap, JavaScript, SPA, and OAuth
2014Suzuki DeutschlandFullStack UI ArchitectPHP, REST API, and JavaScript
2014Deutsche BankFrontend DeveloperEmber.js, HTML5, Grunt, and Bower
2010–2013Deutsche Telekom / Tolino‑AllianzJavaScript DeveloperJavaScript, UnifyJS, PhoneGap, and iOS
2010–2013Deutsche TelekomJavaScript DeveloperJavaScript, qooxdoo, PhoneGap, and iOS
2010Deutsche TelekomMobile DeveloperJavaScript, UnifyJS, and Mobile Cross-Plattform Apps
2008–2009Deutsche TelekomFrontend DeveloperExt JS, JavaScript, and REST API
2007–20083ado AGJava Fullstack DeveloperJava, Spring, Hibernate, and MySQL
2006–2007netz98Frontend DeveloperJavaScript, PHP, Web 2.0, and Affiliate-Integration
2006CommerzbankJava DeveloperJava and SAS
2004–2008DoubleF ITFounder & Managing DirectorLinux, Netzwerktechnik, WLAN, and Server-Administration
2002–2005Technische Hochschule BingenIT System AdministratorLinux, Apache, Mail-Server, and Server-Administration
Sebastian Consulting

Sebastian Software GmbH

Dalheimer Straße 12
55128 Mainz

Amtsgericht Mainz HRB 45232
USt-IdNr. DE295226721

kontakt@sebastian-software.de
www.sebastian-software.de

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As of: March 18, 2026