Senior Frontend Engineer – Design System / Web Components (StencilJS)

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