Full-Stack Developer – AWS / PHP / PostgreSQL / AI Knowledge Platform

UK business is seeking an experienced full-stack developer for an initial paid proof-of-concept, with substantial ongoing work available if the initial project is successful. We are developing a private B2B knowledge and decision-support platform. The application will ingest documents and structured information, provide semantic and natural-language search, return evidence-backed answers, and support a human review and approval workflow. Preferred technology Experience with as many of the following as possible: Python, FastAPI PostgreSQL, pgvector AWS: S3, Lambda and/or ECS, API Gateway React / Next.js REST APIs, Git / GitHub Authentication and role-based access RAG / LLM applications, document ingestion and extraction We particularly want somebody who understands the difference between an LLM and an authoritative knowledge database. The AI must retrieve and reason from controlled knowledge and source evidence — it must not simply generate unsupported answers. Initial Proof-of-Concept Expected to include: document ingestion; structured knowledge records; PostgreSQL database; vector/semantic search; evidence/source storage; natural-language query; AI responses supported by source evidence; basic administrator/review interface; REST API; Git repository; local/development environment; basic automated testing; deployment documentation. The POC will use synthetic/sample data only. The successful developer will not require access to production customer data or our production data storage. Essential requirements Strong full-stack development experience Good written and spoken English AWS experience PostgreSQL/database design experience API development experience Understanding of application security Git/GitHub experience Examples of previous work, and ability to document their work properly Experience with RAG, vector search, document processing, multi-tenant SaaS, audit trails or AI knowledge systems would be particularly useful. How to apply Please begin your application with the word PLACEMENT26. Applications that don't include this may not be considered. Please provide: hourly rate (GBP or USD); normal weekly availability; location and timezone; GitHub/profile/portfolio links; examples of relevant applications you personally developed; which parts of the stack you have personally used; your experience with AWS; your experience with RAG/vector databases/LLMs; whether you work independently or for an agency; and your answer to the following question: “How would you prevent an LLM from answering a question when the underlying knowledge base does not contain sufficient reliable evidence?” This is initially a freelance engagement, but there is potential for substantial ongoing development if the relationship is successful. Individual developers preferred — no recruitment agencies initially.