SaaS & mobile studio · Paris
Your SaaS in production, secure from day one.
We design, build and maintain your product for a fixed price, with a cybersecurity engineer at the helm.
- Fixed price
- Deadlines met
- You own the code
- Security included
- client products in production
- 3
- of the code handed over at delivery
- 100%
- of free maintenance with every MVP
- 30 days
- payment in up to three instalments
- 3×
Technologies we use: Next.js, React Native, Expo, Flutter, Supabase, Stripe, Node.js, Python, TypeScript, PostgreSQL.
Process
A clear framework, from the first call to go-live.
Four steps, a firm price and regular check-ins: you always know where your product stands.
01 · About a week
Scoping & mock-ups
Together, we clarify your needs, your users and the scope. You approve clickable mock-ups and a firm quote before a single line of code is written.
- Written scope
- Approved mock-ups
- Firm price and schedule
02 · The heart of the project
Development with regular check-ins
The product is built in iterations. Every week, you test a version online and share your feedback: you are never left in the dark.
- Online test version
- Weekly check-in
- Transparent progress tracking
03 · Before going live
Delivery, testing and security audit
Before go-live, the product undergoes a full security audit. You receive the code, the access credentials and the documentation.
- Security audit
- Production launch
- Code and access handed over
04 · After delivery
Maintenance & enhancements
The first month of maintenance is free. After that, a monthly plan keeps your product up to date, monitored and ready to evolve.
- 1 month free
- Monitoring and updates
- Monthly enhancements
Security
Security isn't an optional extra. It's part of every project.
Kairn is run by a cybersecurity engineer who analyses applications every day. What is often sold as an add-on is the starting point here.
Robust authentication
Secure sign-in, tightly controlled sessions, roles and permissions checked on the server, never just in the interface.
Each customer's data kept separate
Each customer only sees their own data, guaranteed at the database level and not just by the code.
Up-to-date dependencies
Libraries tracked and kept up to date, known vulnerabilities fixed before they become a problem.
Hosting in Europe
Data hosted in the European Union, secrets never exposed in the browser, backups in place.
An audit before every go-live
A systematic security review before every release, with a report you can show your customers.
This site is the proof
Strict Content Security Policy, hardened headers, no tracking cookies. We practise what we sell.
Vibe-coded prototype?
Need to take an app built with Lovable, Bolt or a freelancer into production?
Our Audit & Hardening package finds and fixes critical vulnerabilities before your first real users arrive. From €1,500 excl. VAT, in 1 to 2 weeks.
Work
Products in production, not mock-ups.
Payments, finance, e-commerce: projects where reliability and security are non-negotiable.
Payment middleware
Hostel20
Middleware that bridges the Beds24 channel manager and the Worldline payment platform, for a network of youth hostels.
- Beds24
- Worldline
- Payments
- Webhooks
Algorithmic trading
SOFinvest
A trading bot that runs strategies across several accounts in parallel, with the reliability that real money demands.
- Trading
- Multi-account
- Automation
- Production
E-commerce
Solidè
A complete e-commerce shop: catalogue, basket, online payment and order management.
- E-commerce
- Online payment
- Catalogue
Pricing
Three packages, each at a fixed price.
You know from the start what you will pay and what you will get. The quote sets out the exact scope.
Audit & Hardening
Your prototype, built with Lovable, Bolt or a freelancer, needs to go into production safely.
From, excl. VAT
€1,500
1 to 2 weeks
- Full security audit of the code and infrastructure
- Critical vulnerabilities fixed
- Clean production launch
- Clear, prioritised report you can read without a technical background
Recommended
SaaS MVP
You have a validated idea and need a solid product for your first customers.
From, excl. VAT
€5,000
5 to 6 weeks
- Complete foundation: login, roles, back office, Stripe payments
- Each customer's data kept strictly separate
- 8 to 10 features specific to your business
- Security by design
- Technical documentation and handover
- 1 month of free maintenance
SaaS + Mobile App
Your product needs to live in your users' pockets.
From, excl. VAT
€9,000
8 weeks
- Everything in the SaaS MVP
- iOS and Android app (Expo)
- Publishing on the App Store and Google Play
- Notifications and an experience designed for mobile
- Firm price, no overruns
- Full transfer of code ownership
- Payment in 3 instalments available
Maintenance
After delivery, we stay by your side.
A live product needs to be monitored, updated and improved. Every MVP includes one month of free maintenance, then you choose the plan that suits you.
Essential
Your product stays online, up to date and protected.
€290excl. VAT / month
- Monitored hosting
- Regular backups
- Security updates
- Bug fixes
Acknowledged within 48 business hours
Choose EssentialRecommended
Growth
Your product keeps evolving every month.
€690excl. VAT / month
- Everything in Essential
- 6 hours of enhancements per month
- Monthly report
Acknowledged within 24 business hours
Choose GrowthPartner
A technical partner committed to your roadmap.
€1,290excl. VAT / month
- Everything in Growth
- 15 hours of enhancements per month
- Quarterly security audit
- Monthly check-in
- Priority on your requests
Blocking issues handled within 24 business hours
Choose Partner
Prices excl. VAT, per month. Unused enhancement hours do not roll over.
Response times are expressed in business hours.
Gabin
Founder of Kairn
About me
A security engineer who builds your products.
I'm Gabin, founder of Kairn. My job is analysing the security of applications. My passion is building them.
Kairn brings the two together: products designed for your users, built to the standards of a banking environment. You have a single point of contact, from scoping to maintenance.
- Education
- Cybersecurity engineer, EFREI Paris
- Day to day
- Application security analyst at a major banking group
- At Kairn
- Full-stack and mobile developer
FAQ
Your questions, answered.
Another question? Ask it during the free initial call.
No, Kairn exists precisely for people like you. We start from your business and your users, not from the technology. Every decision is explained to you in plain terms, and you approve the mock-ups before the first line of code is written.
A live product, the complete source code in your own repository, access to every service (hosting, database, payments), technical documentation and a security report. You are not dependent on anyone, including us.
Yes. Ownership of the code is transferred to you once payment has been made in full. The hosting and service accounts are in your name.
During the project, any out-of-scope request gets a separate quote, which you approve before work starts: the initial price does not change. After delivery, the Growth and Partner plans include enhancement hours every month.
Every MVP includes one month of free maintenance. After that, you can choose a monthly plan: monitoring, backups, security updates, bug fixes and, depending on the plan, enhancement hours.
The price is set in the quote and does not change. Payment is spread over the project and can be made in three instalments. The exact terms are set out in the quote and in our terms of sale.
A SaaS stores your customers' data. A leak means losing their trust, a duty to report it under GDPR and sometimes the end of the product. Fixing things after the fact costs far more than designing them properly from the start: that's why security is included in every project, not sold as an add-on.
A free initial call to scope your project.
A call to understand what you need and tell you honestly what is feasible, and within what budget.