Custom Software IP Ownership and Source Code Assignment: What to Put in the Contract 2026

The verdict in three sentences

Under French law, paying for development does not transfer ownership: without a written assignment clause detailing the rights assigned, their scope, territory and duration (Article L131-3 of the French Intellectual Property Code), the vendor keeps the economic rights to the code. A well-drafted clause costs EUR 1,000 to 3,000 of legal review; a missing one can cost EUR 20,000 to 80,000 the day you want to switch vendors, sell the company or raise funds. The three topics to lock down in 2026 are open source components, the agency's reused modules and reversibility (repository access, documentation, APP escrow).

What the law requires for a valid assignment

Article L131-3 requires each assigned right to be mentioned separately and its field of exploitation to be defined. A sentence like "the client owns the software" is fragile before a judge. For software, you must explicitly cover the rights listed in Article L122-6: reproduction, adaptation, translation, modification, placing on the market, plus the right to sublicense if you plan to commercialise the tool.

Watch out for freelancers too: an independent developer subcontracted by the agency remains the author of their code. If the agency has not obtained an assignment from its subcontractors, it cannot assign you what it does not hold. Demand a warranty against third-party claims and the list of contributors.

The three expensive traps

Open source components. A 2026 application contains 70 to 90% third-party code (frameworks, libraries). That code cannot be assigned: it stays under its licence. What matters is licence compatibility with your use. An AGPL library inside a commercial SaaS may force you to publish your own code. Demand a licence inventory (SBOM) delivered with each release.

The agency's reused modules. Serious agencies reuse internal modules (authentication, billing, back office) to cut lead times. That is legitimate, but those modules are usually licensed, not assigned. Negotiate a perpetual, irrevocable, royalty-free and transferable licence, including if your company is sold.

Reversibility. Ownership without code access is useless. The Git repository must sit on an account in the client's name, with installation documentation and infrastructure secrets handed over at acceptance.

Model clause to adapt

Here is a starting point for your lawyer to validate: "The Vendor assigns to the Client, exclusively, as the work progresses and subject to full payment of the price, all economic rights to the Deliverables, namely the rights of reproduction, performance, adaptation, translation, modification, arrangement, distribution and sublicensing, on any medium and in any form, worldwide and for the full legal term of protection. The assignment price is included in the fixed price of EUR 60,000 excl. VAT. The Vendor's pre-existing Components listed in the appendix are granted under a non-exclusive, perpetual, irrevocable, royalty-free and transferable licence. Open source components remain subject to their licences, inventoried in the appendix."

Mini case study

Laurent, CFO of a 120-employee logistics SME in Nantes, invests EUR 60,000 in a route planning application. The agency's initial contract only grants a "user licence". Cost of renegotiating before signing: EUR 2,000 of legal review and a EUR 1,500 premium accepted by the agency for the assignment, i.e. EUR 3,500 (5.8% of the project). Two years later, an acquirer values the tool as a company asset; without assignment, they would have demanded a discount or a buy-back of rights estimated by the agency at EUR 25,000. Net gain: EUR 21,500, plus the freedom to change vendors.

FAQ

If I pay for all the development, do I own the code?

Not without a written clause complying with Article L131-3. Payment creates at best an implied user licence, often limited to internal use. A contract review at EUR 1,000 to 3,000 removes that risk.

Can the agency refuse the assignment?

Yes, it is negotiable. Agencies generally accept assigning the bespoke code, sometimes for a 3 to 10% premium, and offer a licence for their internal modules.

Is an APP deposit mandatory?

No, it serves as proof of prior creation and as escrow. At EUR 300 to 800 a year, it is justified for strategic code, a commercial SaaS or ahead of fundraising.

What if my current contract says nothing?

Negotiate an assignment amendment with an explicit price, even a symbolic one, and get access to the Git repository immediately. An amendment often costs under EUR 5,000, versus EUR 20,000 to 80,000 for a rewrite.

Are mock-ups and design included?

Only if the clause expressly covers mock-ups, brand guidelines and graphic content. In 1 agency contract out of 2 that we review, they are forgotten.

Let's scope your project. At Kolonell, assignment of economic rights, a Git repository in the client's name and a licence inventory are included in every custom application contract, from EUR 25,000 to 150,000 depending on scope, delivered in 8 to 20 weeks. Detailed quote within 48 h. WhatsApp +221 77 596 93 33.