Do you work with unfunded pre-seed startups?

Yes, under strict conditions: MVP already tested with 5–10 design partners, qualified founder, defensible vision (>€10M ARR in 3 years). Equity-friendly model subject to due diligence.

Who owns the intellectual property of the delivered code?

100% yours. Source code, designs, fine-tuned models, datasets: everything transfers at the end of the project. No vendor lock-in, no exclusivity clause. You can hire your tech team and bring it in-house whenever you want.

How do you handle evolution after go-live?

Three options. Monthly evolution retainer (€1,200–€4,800 excl. VAT/month depending on volume). Sprint-based fee (€8,000 excl. VAT per 2-week sprint). Recruiting and training your internal tech team (Build-Operate-Transfer model).

Which UI frameworks do you use?

Tailwind CSS + shadcn/ui by default (fast, modern, customisable). Material UI, Chakra, or a custom design system depending on your brand. On UX, we work with your team or partner freelance designers.

What about long-term maintenance?

Evolving maintenance retainer from €1,500 excl. VAT/month: monitoring, dependency updates, bug fixes, level-2 customer support. Critical incidents handled within 4 hours on business days.

Can you take over a product already started by another agency?

Yes. We start with a technical audit (3–5 days, €2,800–€4,800 excl. VAT), identify critical debt, and propose a takeover plan. If the code is too degraded, we are honest: sometimes it is better to restart from a clean base.

Is sovereign hosting possible (health, defence, sensitive contracts)?

Yes. Sovereign stack on OVHcloud, Scaleway, or on-premise with self-hosted Mistral Large. No calls to a third-party LLM outside the EU. Timeline +2 weeks, budget +25–40%.

What about AI Act compliance?

Built in from Sprint 0. System classification (limited or high risk), technical documentation, user transparency, continuous monitoring. Documents delivered to your DPO at the end of the project.

Method · AI SaaS Dev4 sprints · 3–6 months · €40–180k

Katalyx Method · AI SaaS Dev

From your AI SaaS idea to your first paying production, in 3–6 months. Without runaway LLM costs. Without hallucinations in production.

Our method for building a SaaS product with LLMs runs on 4 structured sprints. We frame in sprint 0. We build in sprints 1–3. We launch in sprints 4–5. Security, scalability, LLM costs, and hallucinations are handled from day one. Classic fixed fee, equity-friendly, or Build-Operate-Transfer — depending on your maturity.

Discuss my AI SaaS project — 30 min Download our PRD template for AI SaaS

4 sprints · 3–6 months · From €40k to €180k excl. VAT

The observation behind our approach

AI SaaS products do not fail on the feature. They fail on what you cannot see.

8 out of 10 AI SaaS products launched in 2024–2025 failed on 4 predictable issues. Not on functionality. Not on UX. On what stays invisible while the product is in demo — and blows up the moment scaling starts.

The 4 invisible traps our method neutralises from sprint 0:

LLM API costs that explode at scale — a €0.80 marginal cost per active user kills the margin.
Latency that degrades UX — a time-to-first-token > 3 seconds drives users away.
Hallucinations in production — without guardrails, user incidents destroy trust.
Fragile architecture at scale — a product that works for 100 users breaks at 10,000.

Our method exists precisely to address these 4 topics at framing — not as production patches. That is what sets us apart from classic dev agencies that ship an MVP and leave these topics for “later”.

Build what lasts

We build your v1 to last 3 years. Even if you are thinking “MVP”.

Our conviction: even an MVP must be designed for production, not for the demo. Not because we want to over-engineer, but because we have seen too many scale-ups fully rewrite their stack at Series A because of technical debt. That rewrite costs 6–18 months of delay. Unacceptable.

The 3 pillars of our principle:

Pillar 1 — Scaling-ready architecture from sprint 0: stateless, modular, observable.
Pillar 2 — LLM costs modelled before the first line of code: LLM gross margin > 70% required.
Pillar 3 — Security and compliance from sprint 0: GDPR, AI Act, solid auth, RBAC, audit trail.

From PRD to public production

5 sprints. Grouped into 4 phases for clarity.

Phase	Sprints	Duration	Deliverable
Sprint 0 — Discovery & Architecture	1	2 weeks	Full PRD, validated architecture, modelled LLM costs, roadmap.
Sprint 1 — Foundation	1	4–6 weeks	Auth, DB, LLM integrated, first AI feature working in staging.
Sprints 2–3 — Build	2	6–10 weeks	80% of features, private beta with 5 design partners, operational AI guardrails.
Sprints 4–5 — Launch	2	2–4 weeks	Public beta, hardening, go-live, monitoring.

Sprint 0 · 2 weeks · €8,000 excl. VAT (standalone fee available)

Before any code, you validate architecture, costs, and risks. Not after.

Full PRD (12 sections: vision, personas, JTBD, flows, LLM specs, integrations, security, KPIs, risks, roadmap).
Validated stack choice (frontend, backend, LLM, infra, observability).
Architecture diagram + scaling assumptions (target users, requests/day, costs).
Detailed marginal LLM cost model (per action, per user, expected gross margin).
Product + tech risk map with mitigation for each.
Sprint-by-sprint roadmap validated by founders and investors.

Sprint 1 · 4–6 weeks

In 6 weeks, you see your first AI feature working in staging.

Cloud infra setup (Azure EU / AWS Paris / OVHcloud depending on constraints).
Auth + RBAC + multi-tenancy (Clerk, Auth0, or WorkOS).
Database + pgvector for vector search.
Primary LLM integration + fallback + semantic cache.
Design system implemented (standard Tailwind + shadcn/ui, or custom).
First E2E user flow with streaming LLM.
E2E tests + monitoring (Sentry, Langfuse, PostHog).
Operational CI/CD (automatic deploy on push).

Sprints 2–3 · 6–10 weeks

A client demo every 2 weeks. Until it is ready to sell.

Development of the 80% priority features (see Sprint 0 PRD).
Continuous user testing on the prototype (5–10 design partners).
Operational AI guardrails: output validation, human fallback, displayed confidence score.
LLM cost optimisation: smart routing (Haiku/Flash for volume, Sonnet/GPT-4 for quality), semantic cache (40–60% savings).
Security hardening: pen-test, GDPR audit, refined RBAC, full audit trail.
Private beta launched with 5 design partners.

Sprints 4–5 · 2–4 weeks

You go to public production. With foundations to scale to 10,000 users.

Public beta with open sign-ups (waitlist then progressive opening).
Go-to-market plan delivered in parallel (channel recommendations, pricing, sales motion).
Complete user documentation + knowledge base.
Product onboarding refined: time-to-value < 24h.
Production monitoring + alerting: defined SLA, on-call in place.
Post-launch growth plan: 30/60/90-day objectives, KPIs to track.

What no other method addresses in sprint 0

Security, LLM costs, latency, hallucinations, scalability. From sprint 0. Always.

Topic	Katalyx approach
Security	MFA auth, granular RBAC, systematic audit logs, native GDPR, DPAs signed with all subprocessors.
LLM costs	Gross margin modelling in Sprint 0. Smart routing. Semantic cache. Budget guardrails (70/90/100% alerts).
Latency	Streaming by default. Time-to-first-token < 1.2s. Lightweight models for simple tasks. Edge functions when needed.
Hallucinations	Guardrails (Lakera, Guardrails AI). JSON schema validation. RAG when possible. Human fallback on low-confidence cases.
Scalability	Stateless architecture. Async queues (Inngest, Trigger.dev). Edge CDN. Auto-scaling on Vercel / Fly / AWS.

Adapted to your financial maturity

Fixed fee, equity-friendly, or Build-Operate-Transfer. You choose.

Model 1 — Classic fixed fee (€40k–€180k excl. VAT)
For funded scale-ups and software publishers. Firm price, firm calendar, firm deliverable. Our standard model — for 80% of our engagements.
Model 2 — Equity-friendly (reduced fee + 1–4% equity)
For pre-seed founders with a clear vision but a constrained budget. Fee reduced 30–50% against 1–4% equity. Conditions: MVP tested with 5–10 design partners, ambition >€10M ARR in 3 years, founder qualified in tech + product. Subject to due diligence.
Model 3 — Build-Operate-Transfer (6–12 months)
For scale-ups that want a product in production AND to hire their internal tech team in parallel. We build and operate for 6–12 months while you recruit your CTO and first engineers. At the end, full transfer.

Who our method really works for

5 conditions we validate from the first meeting.

MVP tested with 5–10 design partners (you know what you are building).
Founder qualified in tech + product, or an internal senior CTO (not a business-only founder).
Minimum budget €40k, or a viable equity-friendly alternative (defensible vision).
Real ambition (>€10M ARR in 3 years for the classic fixed fee).
Willingness to invest in architecture and quality — not only features.

← See all our methodsExplore our other methods

Same principles. A method adapted to your context.

Google reviews

What our clients say

5.0 out of 5 · 13 reviews

Source: Google

Mohamed Seghir
il y a 2 mois
« Très belle collaboration avec l'équipe Katalyx sur le développement d'iZola. Projet exigeant techniquement (KYC biométrique, signature électronique, scoring), tenue des délais, qualité du code, et surtout un vrai dialogue produit du début à la fin. Un mot pour Victor, notre chef de projet : disponibilité, rigueur, écoute, et cette capacité rare à anticiper les sujets avant qu'ils deviennent des problèmes. Une vraie différence sur un projet de cette ampleur. Merci à toute l'équipe — on continue l'aventure ensemble. À recommander. »
Marie-Anne Falconet
il y a un mois
« Nous avons fait appel à Katalyx pour le développement d'une appli de reconnaissance d'images par IA pour identifier les jouets que nous reconditionnons. Tout le process a été hyper pro, super suivi, documentation détaillée, disponibilité de l'équipe, échanges très fluides. Je recommande vraiment pour tous vos projets, ce sont de vrais experts ! »
Enzo Gauben
il y a 2 mois
« La société Katalyx a permis à notre entreprise de développer et designer notre application iZola de 0. Nous recommandons grandement leur service et leur rigueur qui nous a permis d’avancer en toute sérénité sur le développement de cette dernier de A à Z. Merci à toute l’équipe Katalyx 🤝 Enzo »
Fernandes Denis
il y a 10 mois
« Katalyx nous a accompagné avec une approche très structurée pour développer de nouvelles solutions. Leur compréhension de nos enjeux stratégiques et leur capacité à transformer une idée en plan d’action concret font vraiment la différence. Je recommande vivement pour toute entreprise qui veut accélérer son développement »
Jérôme Staszak
il y a 10 mois
« J’ai eu l’occasion d’échanger à plusieurs reprises avec Enguerrand dans un cadre entrepreneurial. Ce qui m’a marqué, c’est sa capacité à penser “stratégie” avant d’agir, à chercher des solutions concrètes plutôt que des promesses. Son approche est jeune, mais déjà structurée et tournée vers le développement de solutions qui font sens pour les entrepreneurs. Un bel état d’esprit, beaucoup de clarté et une vraie orientation résultat. »

See all reviews on Google

FAQ · AI SaaS Method

Eight founder questions.

IP, equity, maintenance, sovereignty — topics we frame from the first meeting.

01
Do you work with unfunded pre-seed startups?
Yes, under strict conditions: MVP already tested with 5–10 design partners, qualified founder, defensible vision (>€10M ARR in 3 years). Equity-friendly model subject to due diligence.
02
Who owns the intellectual property of the delivered code?
100% yours. Source code, designs, fine-tuned models, datasets: everything transfers at the end of the project. No vendor lock-in, no exclusivity clause. You can hire your tech team and bring it in-house whenever you want.
03
How do you handle evolution after go-live?
Three options. Monthly evolution retainer (€1,200–€4,800 excl. VAT/month depending on volume). Sprint-based fee (€8,000 excl. VAT per 2-week sprint). Recruiting and training your internal tech team (Build-Operate-Transfer model).
04
Which UI frameworks do you use?
Tailwind CSS + shadcn/ui by default (fast, modern, customisable). Material UI, Chakra, or a custom design system depending on your brand. On UX, we work with your team or partner freelance designers.
05
What about long-term maintenance?
Evolving maintenance retainer from €1,500 excl. VAT/month: monitoring, dependency updates, bug fixes, level-2 customer support. Critical incidents handled within 4 hours on business days.
06
Can you take over a product already started by another agency?
Yes. We start with a technical audit (3–5 days, €2,800–€4,800 excl. VAT), identify critical debt, and propose a takeover plan. If the code is too degraded, we are honest: sometimes it is better to restart from a clean base.
07
Is sovereign hosting possible (health, defence, sensitive contracts)?
Yes. Sovereign stack on OVHcloud, Scaleway, or on-premise with self-hosted Mistral Large. No calls to a third-party LLM outside the EU. Timeline +2 weeks, budget +25–40%.
08
What about AI Act compliance?
Built in from Sprint 0. System classification (limited or high risk), technical documentation, user transparency, continuous monitoring. Documents delivered to your DPO at the end of the project.