A product users can log into
Auth, roles, and data boundaries land before the fancy AI layer. You get a real app with accounts, not a public demo that breaks the first time someone shares the link.
AI product development
AI product development for teams that need a product in production, not another demo.
Most AI projects stall after the prototype. You need someone who can take the idea from prompt to production: structured outputs, auth, billing, logging, cost controls, and a codebase your team can maintain. I do AI product development that ships.
80+ five-star reviews · 100% Upwork Job Success · 120+ projects
Zlatko MarjanovicDigital strategist & creative directorBrand Collaborations
7+Years building web and AI products
120+Projects across SaaS, web, and automation
80+Five-star reviews across platforms
100%Upwork job success score
What you get
What changes when this is done right.
Three outcomes I hold myself to before anything ships. If these are not the job, this is the wrong page.
AI that fails safely
Structured outputs, fallbacks, rate limits, and logging so a bad model response does not corrupt data or burn your API budget overnight.
One owner through launch
The same person who scopes the product can build the Next.js app, wire Stripe, set up Supabase RLS, and keep shipping after go-live.
The engagement
What this work actually covers.
Scope first, so you know what you are buying and what stays out.
What this engagement is
I help founders and product teams turn an AI idea, a Lovable prototype, or a half-built agent into software that runs in production. That means architecture, the core product loop, integrations, and the boring infrastructure that keeps it online.
Who it is for
Teams with a clear use case and users waiting, but no one on staff who can own the full stack. If you still need to validate the idea, start with digital strategy. If the prototype works in a demo and dies in real usage, this is the right brief.
What I actually build
Customer-facing AI SaaS, internal copilots, agent workflows with human checkpoints, API integrations with OpenAI, Claude, or Gemini, and the admin tools to monitor what the system is doing. Stack is usually Next.js, TypeScript, Supabase or PostgreSQL, Stripe, and Vercel.
Prototype to production
AI application development is not prompt engineering in a vacuum. Production means idempotent webhooks, eval hooks, cost caps, error states, and a deployment pipeline. I take inherited Bolt, v0, or Cursor builds and harden them instead of starting from zero when the prototype is already close.
AI product engineer versus a generic dev shop
A dev shop will build whatever is in the ticket. An AI product engineer decides what should be deterministic, what should call a model, and where a human has to stay in the loop. That judgment is most of the value in AI product development.
How it works
A sequence, not a scramble.
Same order every time. Discovery, the plan, the build, then the check after launch.
Scope and architecture
We map the user job, the data the model needs, and what has to stay outside the LLM. That kills half the features that would have become maintenance debt.
Days 1-3Product scope, stack decision, and risk list
Core loop in code
Auth, database schema, and the main workflow ship first. The AI layer sits on top of a working app, not the other way around.
Days 4-10Working staging environment with real accounts
Model integration and guardrails
Structured outputs, retries, logging, and admin visibility. We test failure modes before launch, not after a user finds them.
Days 11-16Production-ready AI paths with monitoring
Launch and iteration
Deploy, watch usage and cost, fix the friction that only shows up with real traffic. I stay on for the first production issues instead of disappearing at handoff.
Weeks 3-6Live product plus a backlog ranked by user impact
What the people
have to say
Every review is public and verifiable on
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Zlatko is a PRO! Something I was struggling with for months, took him only a few days. I think I it wasn't for the Christmas holidays, he probably could have completed it with me during our consultation call. He knows how to operate the back end of a website, he understands coding and connection. He is just a life saver and has saved me valuable time. I'll 100% will be working with him as I continue to build my tech business. I recommend him, but be easy on him. I still need him to be available to help me. You can't lose when working with Zlatko! He's excellent!
Meesha Lewis
CEO & Founder at ManeXperience
Working with Zlatko has been nothing but exceptional. From the speed of his work to his deep knowledge of code, the entire process was a pleasure, and I'm very happy with my improved website. Zlatko was responsive, knowledgeable, and willing to go back and forth with me on even the smallest details. He also sent a very detailed video addressing all of my questions and concerns, which I can refer back to for any future updates. I'm very glad I chose Zlatko and would highly recommend him.
Minka Djurasevic
Senior Graphic Designer
Great experience working with Zlatko! He did a great job creating our press sites and delivered a professional, well-structured result that matched what we needed. Communication was smooth throughout the project. Highly recommended and we would happily work with him again!
Hintsteiner Group GmbH
Austria
Very happy with the project and Zlatko's work. I didn't think it was possible but he took my site from a 43 to a 96 score on Lighthouse for page speed and load times. Will definitely be a repeat customer.
Lance Parth
Triton Sensors
Zlatko did a very good job making a new website for my clinic. It looks very professional and streamlined, and I am looking forward to optimizing it for SEO performance. There was a little bit of delay due to some unforeseen issues on his end, but he was communicative and let me know what's going on. I would definitely use him again in the future if needed.
Dr. Farhan Abdullah
CEO at Magnolia Functional Wellness
Zlatko did excellent work on my site. He significantly improved PageSpeed performance, rebuilt a problematic popup natively, and refined the mobile experience so the site is now much smoother and easier to navigate. Communication was clear and professional throughout, and he was thoughtful in addressing both technical performance and real user experience.
Sagel
Yoga and Meditation with Sagel
Zlatko is the real deal. A REAL web developer who builds professional components, structure, and websites. He absolutely knows what he's doing and is the most professional web builder I've worked with on this platform. I will 100% hire him again and again. He's my go-to guy now. Absolutely knocked it out of the park on an insane deadline with a heavily animated and polished build.
Adam
Polyform Studio
The best web developer you could ever ask for, he did an amazing job with our website and we will be working with him in the future for more projects. We are extremely satisfied with his work and the end result. Highly recommend you Zlatko for any high end website needs.
Alexander Karima
Co-founder at Mavesta Media
Zlatko did such an amazing job fixing up my site. He is always fast and responsive and delivers high-quality work. Will definitely come back again. Highly recommend.
Dana Yao
Senior Product Designer at Visa Inc.
Zlatko is very experienced, able to communicate clearly and efficiently and able to work very fast while still delivering quality work. He's an amazing web designer and I will definitely be back for future work and refer close friends to his offer.
Astral Labs Agency
Independent Employer
Zlatko has been a pleasure to work with. He is extremely professional, proficient and articulate. He met our tight deadline and was incredibly patient with our changes. Looking forward to working with him in the future.
Matthew John S
CEO at Gsshades
Zlatko exceeded in every possible way. Excellent communicator, very speedy in response and proactively thinking with me to get the most out of my website and setup. He is a gem!
Desiree Kolman
Personal Website Build
Zlatko was extraordinarily ADEPT, EFFICIENT and provided amazingly high quality in his work. Would HIGHLY recommend him!
Nick Maciel
Founder at Cadversity
Zlatko is hard-working and proactive, with excellent communication skills and a keen eye for detail. We engaged Zlatko to help with a broad range of tasks with quite a short turnaround, and we couldn't be happier with his results. I highly recommend his services and would not hesitate to work with him again in the future.
Thom Vaughan
Manager at Common Crawl
Zlatko was incredible to work with, he helped spin up our website in less than two days and responded within minutes to all of my requests. Can't thank him enough, will use him again for many other projects moving forward. My second time working with him in 2 weeks and he's completely exceeded expectations yet again.
Marina Paganessi
Co-Founder at Focus&Film
Zlatko was a dream to work with and we would 100% work with him again!
Dominique De Leon
Independent Employer
Great job. Did a comprehensive overhaul of our entire site and got us to move off SquareSpace. Very collaborative and consultative, which was very helpful.
Seth Meritt
CEO at Welby Health
Zlatko is a true pro. His knowledge of web development is tremendous, and he is very committed to ensuring everything works to your satisfaction before delivery. I will continue to be using Zlatko for any updates to my website, and cannot recommend his services enough!
Zach Garti
Founder of Pareidolia
Our website allows us to deliver our vision, impact, and connect with our existing and future community around the world. Thanks to Zlatko's skillsets and laser-focused diligence, it speaks to our audience, inspires others to take action, and transmits the energy of our work with young founders.
Filip Sasic
CEO & Founder at EGC
I had the pleasure of working with Z on a project, and I couldn't be more impressed with the results. His communication is exceptional, clear, prompt, and always professional. Z truly understands client needs and goes above and beyond to ensure satisfaction. I look forward to collaborating with him on future projects.
Jordan W. Bryant
Chair & CEO, Vault Apps
Zlatko was incredible. He worked diligently under a deadline, gave incredible insights and was able to work on his own and bring massive value to the project. It was a pleasure working with him on this project and will be working with him again in the future. Best web person I've worked with on this platform, by far.
Marshall Wilkinson
CEO, Construct
He did a great job and completed the website very quickly. Excellent designer and good communicator.
Jeremy Brown
CEO at Karihub
What is included
What lands on your side.
The artifacts you keep after the call, the build, or the audit.
Product and technical scope
What ships in v1, what waits, and what never should have been an AI feature in the first place.
Production codebase
Next.js or your chosen stack, typed, deployed, and documented enough that another engineer can pick it up.
Auth, billing, and permissions
Supabase auth, Stripe subscriptions or usage billing, and RLS or role checks where customer data is involved.
LLM integration layer
Prompts, structured outputs, fallbacks, and cost controls wired into the product, not pasted into a notebook.
Observability and admin tools
Logs, error tracking, and internal views so you can see what the system did when something looks wrong.
Launch support
Deployment, smoke tests, and the first round of fixes after real users hit the product.
Before we start
Questions about this work.
Short answers so you can tell if this is the right engagement.
No. A lot of my work is taking an existing Lovable, Bolt, or v0 prototype and making it production-ready: auth, database, billing, error handling, and deployment.
OpenAI, Claude, and Gemini depending on the task. For orchestration I use n8n or code-first workflows in TypeScript. The model is a component, not the whole architecture.
Yes. New features, copilots, internal tools, and agent workflows that sit next to your current stack. I read the codebase first and ship the smallest useful slice.
Not as a standalone engagement. Prompts matter, but AI product development is the app around them: data, auth, UX for failure states, and ops. Prompt-only work does not survive contact with users.
Structured outputs, caching where it helps, rate limits, fallbacks, and logging. We set cost expectations before launch and wire alerts so a traffic spike does not surprise you on the API bill.
Next.js, TypeScript, Supabase or PostgreSQL, Stripe, Vercel. I match your stack when the product already exists. The goal is software your team can maintain, not a pile of no-code glue.
A focused v1 with one core workflow is often three to six weeks. Inherited prototypes can move faster. Scope always depends on auth, billing, and how messy the data model is.
Yes, on retainer or project basis. The first month in production always surfaces edge cases. I would rather fix them with you than hand you a demo and disappear.
AI product development is building software where AI is part of the user experience, with the same production standards as any other app: accounts, data, billing, monitoring, and a codebase that can evolve.
You work with one AI product engineer who scopes, builds, and ships. No handoff between a strategist, a prompt person, and a dev team that never talked to your users.
Related services
Other ways I can help.
Same person, same commercial standard. Different entry point.
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