Diagnose
AI Feature Review
We go through up to three of your AI flows the way a new user would, check them against the Article 50 transparency duties, and give you a ranked fix list with a recorded walkthrough.
AI development agency in Europe
Fessburn is an AI development agency in Poland that designs and builds AI features
We're a product studio in Warsaw and Poznań. We design and build AI features for products that people rely on at work, like clinical tools and finance apps, and we take on projects from teams across Europe and the US.
The same team runs the research, designs the screens, and writes the production code. Every project has a fixed price for the scope we agree on in writing.
- Based in
- Warsaw and Poznań
- Founded
- 2006
- Google rating
- 5.0 from 25 reviews
- Smallest project
- From €5,500
Why an AI feature that works in a demo can fail with real users
A demo is a simulated environment. No matter how much you try to simulate, you choose the input, and you know the expected outcome based on the inputs you created. On the other hand, real users paste in messy data and take answers at face value, thinking it's the correct one.
So when we build an AI feature, we design the failure modes first: the screen people see when the model returns a wrong or empty answer, and the way they can recover from it. We also design how the product lets people know they're dealing with AI, because Article 50 of the AI Act has required that since 2 August 2026.
Which AI projects do we take on?
Each of these has a fixed price and a set length. The prices are the starting points from our own site.
Diagnose
Product Readiness Review
You built your MVP with a tool like Lovable or Cursor, and real users are signing up. We review the UX, the architecture, and the security basics, and tell you if we'd fix the app or rebuild it.
Prove
Evidence Sprint
We build the one flow you're least sure about as a working app on a live URL, with live AI calls where the flow needs them, and test it with 5 to 8 people from your user group.
Build
Build
We design and build web and mobile apps for iOS and Android, with the AI disclosure and recovery states designed in, and release to a staging URL every week.
Build
Private AI Setup
We install an AI assistant on a server in your office, so your clients' files are processed on your own hardware instead of by an AI provider. It's set up for teams like law firms and medical practices.
Which EU AI Act dates apply to an AI feature?
If you sell into the EU, the AI Act sets the dates your product has to meet. These are the ones we plan our AI work around. They're dates from the regulation, and this isn't legal advice.
| Rule | Date | What it means for your product |
|---|---|---|
| AI Act Article 50 transparency | Since 2 Aug 2026 | People have to be told when they're interacting with an AI system. |
| Marking AI-generated content | 2 Dec 2026 | Generative systems already on the market have to mark the content they produce. |
| High-risk AI systems | 2 Dec 2027 | Stand-alone high-risk systems take on the AI Act's full obligations, including human oversight. |
| AI in regulated products | 2 Aug 2028 | AI built into regulated products, including medical devices, takes on the high-risk obligations. |
AI and product work we've done for clients
AI product
AiListz
AiListz opened on a blank prompt box, and new users didn't know how to start. We designed the onboarding, the conversational guidance, and the controls. Support requests from first-time users dropped by 90%.
Our own product
InvoiceRate
We designed and built InvoiceRate, a KSeF invoicing app that 3,000+ people use. It's only connected to KSeF through an API, so we designed the screens people see when KSeF rejects an invoice.
Critical care
Bayer
For ICU Angel, Bayer's ARDS risk-monitoring platform, we ran moderated prototype testing across the whole workflow. Clinicians went from about 30 seconds to less than 5 seconds to spot a critical change.
How do you choose an AI development agency in Europe?
These are the questions we'd ask if we were hiring a studio for an AI feature. They work for any agency you talk to, including us.
- Ask to see an AI feature they shipped to real users, and what happened after launch. A demo video is a simulated environment, so it won't show you the failure modes.
- Ask how they design the recovery path when the model returns a wrong answer, and how the product lets people know they're dealing with AI.
- Ask who writes the production code. If design and development are two companies, the designer's reasons for a decision often don't make it into the code.
- Ask where your data is processed. If you handle confidential client files, you can keep them on your own hardware with a private setup.
- Ask how the price is set. A fixed price only works when the scope is written down at the start, so ask to see the scope document.
Questions people ask us
Where is Fessburn based?
We work from Warsaw and Poznań in Poland, and we take on projects from teams across Europe and the US. We work asynchronously in the files and repository you already use, with a written update every week.
Can we try you on a small piece of work first?
Yes. Send us one AI flow and one question. Within 5 business days, you'll get a free recorded walkthrough and a one-page fix list, and we'll tell you straight if a bigger project makes sense.
How do payments work?
You pay 50% at kickoff and 50% on delivery. Once we've agreed on the scope, the price is fixed.
Can we sign an NDA first?
Yes. If you need one before sharing files, send it with your first email to hello@fessburn.com.
Do you give legal advice on the AI Act?
No. We design the disclosure and recovery states in your product and check them against Article 50, and your legal team signs off on compliance.
Send us the AI feature you're working on
Write to us with the feature and the question you most need answered. We'll reply with the project we'd recommend and its fixed price.