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Sebastian Consulting
Sebastian Fastner
Sebastian FastnerDiplom-Informatiker (FH)

24 Jahre Softwareentwicklung hinterlassen Spuren – in meinem Fall Produkte, die in über zehn Ländern laufen. Bei der DWS Group habe ich eine Investmentplattform gebaut, die europäische und asiatische Märkte bedient. Bei Witt die technische Grundlage für 17 Online-Shops gelegt. Für Regrello eine KI-Übersetzungspipeline entwickelt, die Nutzer verschiedener Sprachen nahtlos zusammenarbeiten lässt.

Zuhause bin ich in TypeScript und React. Dazu kommt ein Tooling-Stack, der zeigt, dass Frontend längst mehr ist als Oberfläche: Vite, Vitest, Playwright, Infrastructure as Code, CI/CD. Aber Technologie allein interessiert mich wenig. Was mich umtreibt: Architekturen, die wachsen können, ohne unter ihrem eigenen Gewicht zusammenzubrechen. Code, der auch vom nächsten Team verstanden wird. Und die ehrliche Einschätzung, wann ein neues Tool echten Mehrwert bringt – und wann es nur Komplexität addiert.

Bei Sebastian Software bin ich als Senior Technology Consultant dort unterwegs, wo Frontend-Architektur, Mobile und Internationalisierung sich überschneiden. Nicht als externer Dienstleister, der Code abliefert, sondern als Partner, der Wissen teilt und Teams weiterbringt.

Kernkompetenzen

TypeScriptReactReact RouterVanilla ExtractConvexNode.jsCloud-InfrastrukturInfrastructure as CodeViteVitestPlaywrightCI/CDGraphQLTemporal

Persönliche Daten

Standort
Mainz, Germany
Zusammenarbeit
bevorzugt Remote + gelegentlich vor Ort
Sprachen
Deutsch und Englisch
Staatsangehörigkeit
Deutsch
Kontakt
s.fastner@sebastian-software.de
Telefon
+49 176 32042696

Branchenerfahrung

10
Telekommunikation
7
Fintech
3
E-Commerce
2
Enterprise Software

Mein 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

Projekterfahrung

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

Weitere Projekte

Deutsche TelekomJako-oSuzuki DeutschlandDeutsche Bank3ado AGnetz98CommerzbankTechnische Hochschule Bingen
ZeitraumKundeRolleTechnologien
2016Deutsche TelekomSenior Application ArchitectAngularJS, HTML5, PhoneGap und OAuth2
2015–2016Jako-oLead Application ArchitectJavaScript, SPA, REST API und Mobile-Optimierung
2015Deutsche TelekomLead Application ArchitectPhoneGap, JavaScript, SPA und OAuth
2014Suzuki DeutschlandFullStack UI ArchitectPHP, REST API und JavaScript
2014Deutsche BankFrontend DeveloperEmber.js, HTML5, Grunt und Bower
2010–2013Deutsche Telekom / Tolino‑AllianzJavaScript DeveloperJavaScript, UnifyJS, PhoneGap und iOS
2010–2013Deutsche TelekomJavaScript DeveloperJavaScript, qooxdoo, PhoneGap und iOS
2010Deutsche TelekomMobile DeveloperJavaScript, UnifyJS und Mobile Cross-Plattform Apps
2008–2009Deutsche TelekomFrontend DeveloperExt JS, JavaScript und REST API
2007–20083ado AGJava Fullstack DeveloperJava, Spring, Hibernate und MySQL
2006–2007netz98Frontend DeveloperJavaScript, PHP, Web 2.0 und Affiliate-Integration
2006CommerzbankJava DeveloperJava und SAS
2004–2008DoubleF ITFounder & Managing DirectorLinux, Netzwerktechnik, WLAN und Server-Administration
2002–2005Technische Hochschule BingenIT System AdministratorLinux, Apache, Mail-Server und 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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Stand: 18. März 2026