BACK TO AI App Development

Custom AI Web Application – Full Stack AI Engineer

Full web application with a built-in AI engine. Authentication, database, admin panel, API integrations, and AI as a core feature — not an add-on.

SERVICE DETAILS

I build custom AI software — fully-featured web applications where AI is integral to the product, not a bolted-on chatbot. Typical project: React/Next.js App Router (frontend), FastAPI or Node.js with Express (backend), PostgreSQL or Supabase (database), LLM integration via LangChain or direct API. I deliver authentication (NextAuth/Auth0), admin panel, role and permission system, external API integrations, and full unit and integration test coverage. Full stack AI engineer — projects from Warsaw to Berlin and Amsterdam.

> INVESTMENT:

from €8,000
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Key Benefits

SaaS or internal tool with AI as a core feature — not a chatbot bolted onto existing software, but AI integrated into every layer of the product.

Custom AI software you own outright — code in GitHub, no vendor lock-in, free to develop with any engineering team.

Full test coverage: unit, integration, and E2E tests with Playwright — you can add new features without fear of regression.

Admin panel, user management, roles, and permissions — ready for your operations team from day one after launch.

Technical documentation and ADRs (Architecture Decision Records) — your next developer understands design decisions without a week of onboarding.

The Process

1

Requirements and architecture

2-3 day discovery workshop: user story mapping, technology stack selection, database design, and AI system architecture. I deliver a technical specification before the first line of code.

2

Backend, database, and AI engine

Building the foundation: API (REST or GraphQL), database schema, authentication, and AI pipeline. This phase takes 3-5 weeks and is the most critical for performance and security.

3

Frontend and end-to-end integration

React/Next.js with UI components (Radix UI or Shadcn), API connection, error handling, and loading states. I iterate based on feedback on a live staging environment via Vercel Preview Deployments.

4

Testing, hardening, and launch

Automated testing, security audit (OWASP Top 10), monitoring setup (Sentry, Datadog), and production launch. I deliver an operational runbook and a code handover session.

Frequently Asked Questions

What does collaboration look like on a project?

I work in 2-week sprints with daily updates via Slack and weekly live demos. You have access to the repository, a Linear board, and the staging environment throughout the entire project.

Do you offer post-launch maintenance?

Yes — a maintenance retainer (bug fixes, dependency updates, monitoring) from €600/month. One-off feature additions beyond the application contract are also possible.

Do you work with an existing codebase?

Yes, if the codebase is in reasonable technical shape. I start with a code audit before quoting the project. Refactoring and extending an existing application are priced separately.

What is 'custom AI software' and 'full stack AI engineer'?

Custom AI software is an application built specifically for your business, not an off-the-shelf SaaS with your logo. Full stack AI engineer — I work remotely with clients across Europe and am available for meetings in the Central European time zone (CET).

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More from this service

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Working AI application prototype in 4-8 weeks. Concept validation, core features, ready to show investors and first users.

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AI Systems Programming – Backend, API & AI Engine

Dedicated backend and API for your AI system. Microservices architecture, AI model integration, scaling to millions of requests, and readiness for future extensions.

View module
All modules of AI App Development

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BIAŁYSTOK, PL
+48 732 022 086pawel.wiszniewski95@gmail.com