We are looking for a Senior Frontend Engineer – Design System / Web Components (StencilJS) for a large German product company. It’s built with Web Components on StencilJS and used by several product teams across different frameworks. The work covers the library’s architecture and packaging, server-side rendering, and AI-assisted development processes. You need to understand how each change affects the whole product and the teams that integrate the library.
Details: 📍 Remote, with about 1 onsite day a month in Stuttgart, Germany
📄 B2B contract / freelance
Start: ASAP English: Fluent
Tech stack: StencilJS 4, TypeScript, HTML/TSX, JSS, Tailwind CSS · Angular, React, Next.js, Vue · npm workspaces, Rollup, Vite, Webpack · Vitest, Playwright, axe-core · Agent Skills, MCP, GitHub Copilot · GitHub Actions, AWS CloudFront
What you’ll do
Refactor and modernise the component library (StencilJS 4, TypeScript)
Replace CDN-based delivery with bundler-friendly packages, keeping breaking changes to a minimum and providing clear migration paths
Support React Server Components and streaming in Next.js (App Router), plus SSR for Vue within Astro
Solve Web Components / Shadow DOM boundary issues, Declarative Shadow DOM and hydration
Develop agent skills, MCP servers and a shared source of component metadata, examples and docs that generates documentation, types and AI tooling
Build agentic workflows for code reviews, changelogs, dependency updates and documentation
Ensure accessibility and quality, and support the integrating teams in writing and by phone
Must-have
Several years building design systems or component libraries
Strong hands-on Web Components / StencilJS, Shadow DOM, Declarative Shadow DOM, Constructable Stylesheets
Strong TypeScript, semantic HTML, modern CSS and modern browser APIs
Solid React and Next.js: App Router, Server Components, streaming, hydration
Library packaging: ESM-only, exports maps, tree-shaking, Rollup, Vite, Webpack
npm workspaces, monorepos, semantic versioning, deprecations and migration strategies
AI-assisted development workflows: MCP, agent skills, prompt and context engineering
Accessibility to WCAG 2.2 AA: keyboard, ARIA, forced colours, screen-reader testing
TDD, with unit, E2E, visual-regression and accessibility tests; CI/CD with GitHub Actions
Agile, end-to-end product lifecycle; independent, long-term product mindset
Good written and spoken English
⚠️ Experience building only React/Next.js applications isn’t enough for this role. Hands-on StencilJS / Web Components work is essential.
Nice to have
Angular and Vue
German
