Full-Stack Developer (Next.js/NestJS/Supabase) — Climate-Tech Marketplace MVP, Phase 0-1

We are seeking a skilled developer with expertise in Supabase RLS, Next.js, n8n workflow automation, NestJS, and PostgreSQL for platform development. The ideal candidate will have experience in backend technologies and be able to work on complex projects. This is a part-time role with a project scale of medium, expected to last 1 to 3 months. We are building a B2B marketplace platform connecting companies with vetted energy/climate consultants and implementation partners — think a structured, AI-assisted matching process from initial company analysis through to project completion. The architecture, database schema, API contracts, and all 26 core workflows are already fully specified in a complete internal technical handbook (~250 pages) — your job is to build against that specification, not to design it from scratch. What's already decided (you will not need to make these calls): Full tech stack: Next.js/TypeScript (frontend, Vercel), NestJS/TypeScript (backend), PostgreSQL via Supabase incl. pgvector, n8n (self-hosted workflow orchestration), Cloudflare, Stripe, Mailjet, Docker/Coolify deployment, GitHub Actions CI/CD, Grafana/Prometheus/Loki observability, Hetzner Cloud (EU hosting). Complete database schema definitions, REST API contract (38 endpoints, request/response/roles/error codes), and workflow-by-workflow specification (trigger, steps, error handling, fallback, escalation, logging, monitoring) for all 26 core workflows. Role-based access model (5 roles), Row-Level Security approach, admin action hardening (step-up auth, four-eyes principle). What you will do (phased delivery): Phase 0: Stand up the infrastructure (DB schema, backend skeleton, security layer, CI/CD, monitoring, backup) from the provided spec. Phase 1: Build company/consultant/provider registration and the qualification workflow. Phase 2: Build the AI-assisted analysis, funding-eligibility check, and matching engine integration. Phase 3: Build the offer comparison, award, project execution and completion flow. (Phase 4, learning cycle & GDPR workflows, to be scoped separately after Phase 1-3 are delivered.) Recommended approach: We're open to discussing a leaner initial release — e.g. Phase 0-1 plus a simplified Phase 3 without the AI-matching layer (rule-based/manual matching for launch, AI matching as a fast-follower), and a reduced role model at launch. If you see a faster path to a working marketplace core, tell us in your proposal. Full specification is shared under NDA after an initial screening call — see application questions below. This is a serious, well-documented project: you will receive a complete technical handbook, not a vague brief. We're open to: individual full-stack freelancers or small agencies/teams. Please indicate which you are in your proposal. Budget: Fixed-price milestones per phase, or hourly — open to discuss based on your proposal. Phase 0-3 core process. Duration: Estimated 4 months for a reduced Phase 0-1 launch scope; 6–9 months for the full Phase 0-3 core process. Before contract award: Shortlisted candidates will be asked to complete a small paid test task (2-3 hours, compensated) implementing one endpoint against a sample from our API contract. This lets both sides confirm fit before committing to the full engagement. Please note: Only apply if you meet ALL the criteria listed above under "Ideal candidate." This is an Expert-level engagement — we will not consider applications from beginners, students, or freelancers without proven production experience in this exact stack. Generic or templated proposals will be rejected without response. Ideal candidate: Proven production experience with Next.js, NestJS (or comparable Node.js backend framework), PostgreSQL Experience with Supabase (Auth, Storage, RLS) a strong plus Experience with n8n or comparable workflow-automation tools a strong plus Comfortable working from a detailed written specification and asking precise clarifying questions rather than guessing Clear, proactive English communication (async-friendly, since client is in Europe — time zone overlap is a plus but not mandatory) Skills (tags, max. 10) Next.js, NestJS, TypeScript, PostgreSQL, Supabase, REST API Development, Docker, CI/CD, n8n, Row-Level Security Project length 4 months (reduced Phase 0-1 launch scope); option to extend to 6-9 months for full Phase 0-3 Experience level Expert Screening Questions: To confirm you've read the full job post, please start your proposal with the word "Handbuch." Have you built a production system using Supabase Row-Level Security with multiple user roles? Please share a GitHub link or code sample demonstrating this. This project is built entirely from a pre-written 250-page technical specification (DB schema, API contracts, workflow definitions already fixed). How do you typically work when the architecture is already decided rather than designed by you? What's your process for asking clarifying questions vs. making assumptions? Link your GitHub profile (required, not optional). Which of your public/private repos best demonstrates NestJS + PostgreSQL backend work? Have you used n8n (or Temporal/Zapier/Make) for backend workflow orchestration? If yes, briefly describe one workflow you built. Describe a bug you introduced in production and how you caught/fixed it — what would you change in your testing process next time?