Mathieu Haye is a freelance builder based in Paris who designs and ships custom web apps, AI agents and CRM automations, from spec to production, in a matter of weeks. One person scopes, codes, deploys and maintains. Three formats exist: a 1-week Sprint, a 4-to-6-week MVP, and a monthly Retainer.
Key facts
- A freelance builder, not an agency: you talk directly to the person who writes the code, with no project-manager in between.
- Three packages: 1-week Sprint (from 400 EUR), MVP 4 to 6 weeks on quote, monthly Retainer on quote.
- Modern stack: Next.js, Supabase, Stripe, n8n and AI agents on the OpenAI or Claude APIs, with Claude Code as pair-programmer.
- Focus areas: custom web apps, n8n automation, Salesforce integration and fixes, business AI agents, and AI visibility (GEO).
- You own the code: Git repository, admin access, clear documentation, no hidden dependencies.
How does a project with a freelance builder work?
A project starts with a 30-minute scoping call over video, where the perimeter and the expected outcome are defined. A written quote follows, then the build, with one single point of contact throughout: the person who scopes is the one who codes, deploys and maintains. On a Sprint, delivery lands within 5 business days. On an MVP, the scope is sliced into a usable V1 that you get your hands on before any iteration. You keep direct access (phone, shared Slack or Notion), with no account manager filtering you. For the technical steps, see the AI maturity grid.
How much does a custom app or an automation cost?
The price depends on scope, framed in 30 minutes. A 1-week Sprint (one n8n workflow, a simple AI agent, a Salesforce fix) starts from 400 EUR. A full MVP, with user base, payments and production deployment, is set on quote depending on scope, typically over 4 to 6 weeks. The monthly Retainer is priced by the number of reserved days, in practice 4 to 8 days per month. The figures shown are honest orders of magnitude: the final quote is fixed once the need is clear, with no surprises along the way.
How long does it take to deliver an MVP?
An MVP is delivered in 4 to 6 weeks in most cases. The method is MVP-first: the target is a genuinely usable V1 (authentication, main flow, payments if needed), deployed to production, then iterated after real-world use rather than before. That velocity comes from a modern stack and Claude Code as pair-programmer, which speeds up typing and documentation. A standalone Sprint ships in 5 business days. The exact timeline depends on the perimeter agreed during scoping.
What is the difference between a freelance builder and an agency?
A freelance builder saves you the structural overhead of an agency, which often bills 3 to 5 times more to fund salespeople, project managers and back-office. With a builder, you talk directly to the person who produces the code, which shortens decision loops and avoids losses in translation. Mathieu covers scoping, simple design, frontend, backend, infrastructure and AI-agent integration on his own, where a classic freelancer is often single-stack. For a product that needs more than ten developers in parallel, an agency remains the better fit; for an MVP, an internal tool or an automation, the freelance builder is faster and more economical.
What if I don't know exactly what I need?
That is the most common situation, and it is not a problem. You do not need a written spec to start: just explain the outcome you are aiming for, even in plain business terms. The 30-minute scoping call exists precisely to turn a fuzzy idea into a clear perimeter, to separate what really matters from what can wait, and to pick the right format (Sprint, MVP or Retainer). You leave that call with an honest recommendation and an order of magnitude, with no commitment. If the project is not ready or falls outside my skill set, I tell you plainly and point you in the right direction, rather than selling you something that does not fit.
Frequently asked questions
Do we need to sign a contract before starting?
Yes. Every engagement starts with a written quote and, if you want, a signed NDA before any detailed discussion about your product. The Sprint and the MVP come with a clear purchase order; the Retainer with a monthly agreement. Nothing begins on a verbal handshake alone.
What tools and technologies does Mathieu work with?
The default stack is Next.js for the web, Supabase for the database and authentication, Stripe for payments, n8n for orchestration and automations, and AI agents built on the OpenAI or Claude APIs. On the CRM side, Mathieu works mainly with Salesforce. Claude Code acts as a pair-programmer across the whole project.
Who owns the code produced during the engagement?
The code is yours. You get a Git repository you own, admin access and clear documentation. Everything is transferable to another team with no hidden dependencies, at any time.
Can Mathieu plug into an existing tech team?
Yes. Mathieu often works as an additional builder on a focused topic (AI integration, CRM rebuild, n8n automation), alongside an existing team. Collaboration runs through a shared Slack or Notion and a short weekly check-in.
Do you work with clients outside Paris?
Yes. Mathieu is based in Paris but works remotely with clients across France and internationally. Exchanges happen over video, code and documentation are available online, and English calls are fine for both scoping and demos.