AI-Assisted Full-Stack Builder – German Voice Agents, Mobile Apps & Client Websites

nüll is a German digital agency building websites, applications, and AI-powered customer-acquisition systems for tradespeople, consultants, law firms, and local businesses across Germany.

We are looking for a resourceful AI-assisted full-stack builder who can figure things out, learn unfamiliar tools quickly, debug problems, and ship complete working products. We actively use Claude Code, Cursor, OpenAI Codex, ChatGPT, and other AI development tools. You do not need to know every platform before starting, but you must understand code well enough to review, test, secure, and improve AI-generated work.

This is not a role for someone who waits for detailed step-by-step instructions. You should be comfortable reading documentation, testing APIs, solving blockers independently, and taking a project from idea to production.

THE THREE TYPES OF WORK

1. German AI Call Agents
You will build German-speaking AI telephone agents for tradespeople and local-business owners. Use cases may include inbound call answering, lead qualification, appointment booking, missed-call recovery, FAQs, follow-up, call transfers, and CRM updates.

You should be able to research and work with platforms such as Vapi, Retell AI, Twilio, ElevenLabs, OpenAI Realtime, or comparable tools. You must be able to connect telephony, speech recognition, German text-to-speech, webhooks, calendars, CRMs, databases, and analytics.

The call experience must work naturally in German. You should be able to test pronunciation, latency, interruptions, silence, dates, phone numbers, names, addresses, appointment flows, transfers, and failure handling. Perfect German fluency is helpful but not mandatory if you can work accurately with supplied German scripts and our German-speaking reviewer. GDPR-aware implementation and safe handling of recordings, transcripts, and customer data are required.

2. Real Mobile Applications
You must have contributed to at least one real mobile application currently available on the Apple App Store. Live App Store links are mandatory.

We need proof of what you personally built. For every app you submit, explain your exact role, technologies used, features implemented, and whether you handled TestFlight, App Store Connect, signing, release management, or production maintenance.

Relevant experience may include React Native, Flutter, native iOS, authentication, APIs, databases, push notifications, subscriptions, payments, analytics, and crash reporting. Screenshots, Figma designs, tutorials, local demos, and unfinished prototypes do not replace a live App Store application.

3. Client Websites
You will build polished, conversion-focused websites for our German clients, similar in quality to the work our current developer Raemer produces.

You should be comfortable with React, Next.js, TypeScript, Tailwind CSS, Supabase, APIs, GitHub, and Vercel. Typical projects include responsive 5–10 page business websites, landing pages, lead forms, booking flows, email notifications, CRM integrations, analytics, conversion tracking, technical SEO, and performance optimization.

You must have enough visual judgment to turn a brief or reference into an original, professional design without always receiving a complete Figma file. The result must be responsive, tested, maintainable, and ready for a real client—not an unfinished AI-generated prototype.

HOW WE WORK

• Use AI coding tools to increase speed while remaining responsible for the final result
• Research unfamiliar APIs and platforms independently
• Communicate blockers early and provide concise progress updates
• Connect billed hours to visible tasks and deliverables
• Test your own work before requesting review
• Deliver source code to agency-owned GitHub repositories
• Document setup, environment variables, integrations, and deployment
• Protect client information and credentials
• Do not subcontract work without approval

WHO SHOULD APPLY
We care more about shipped products, practical judgment, and problem-solving ability than formal titles. You should apply if you can demonstrate that you have built real products, understand the code you produce, and can figure out unfamiliar technical problems as you go.

Do not apply if your experience consists mainly of tutorials, certificates, school projects, copied templates, WordPress page building, or AI-generated demos that were never used in production.

APPLICATION REQUIREMENTS
Begin your application with the word BERLIN. Answer every question directly and number your answers. Generic applications without proof will be skipped.

1. Attach or link your current résumé/CV.
2. Provide direct links to all Apple App Store applications you personally helped build. For each app, state your exact contribution and the technologies used.
3. Did you personally handle TestFlight, App Store Connect, signing, releases, or production maintenance? Explain.
4. Provide a live demo, recording, or case study of an AI voice or telephone agent you built. State the telephony, voice, model, and integration stack.
5. Have you built a German-speaking call agent? If yes, provide evidence. If not, explain exactly how you would build and test one.
6. Explain how you would test German pronunciation, interruptions, dates, phone numbers, addresses, appointment booking, call transfers, and failure handling.
7. Provide at least five live websites you personally developed. Explain what you built on each website.
8. Describe your experience with React, Next.js, TypeScript, Tailwind, Supabase, APIs, GitHub, and Vercel.
9. Which AI coding tools do you use, and describe one difficult problem you solved with them.
10. Give an example of a technology you did not know beforehand but successfully learned and shipped.
11. Confirm your time zone, weekly availability, expected compensation, and earliest starting date.

Portfolio ownership and technical claims will be verified during a live interview using hypothetical scenarios and discussion of your existing work. There is no paid trial task.