Can You Copy Game Mechanics? What Is Free and What Is Not

Copyright generally lets you build your own game on a mechanic you saw elsewhere, because it does not protect ideas or rules as such. It does not let you take code, assets, text or the specific look, names are protected by other rights, and a patent or contract can restrict even what copyright leaves open.

This is general information about categories of material. It is not a statement that any specific mechanic is free to use, and it is not a guide to rebuilding someone else's game.

What does copyright usually leave open?

Under EU law the ideas and principles behind a program are not protected, and neither is its functionality as such (details and cases). US law excludes ideas, systems and methods of operation. In practice, copyright usually leaves these open:

• a general idea or genre;
• how a system behaves in general terms, as far as that is an idea or rule;
• what you learn by playing a copy you are entitled to use. Article 5(3) of the Software Directive allows you to observe, study and test a program while doing what you are entitled to do with it, and Article 8 makes contrary contract terms void.

In Germany there is a limit to note: a sufficiently original game flow set down in written rules may be protected, as explained on the copyright page. And all of this is copyright only. It says nothing about patents.

What can you not take?

• Code. Source and object code are protected. Taking the code that implements a feature can be partial reproduction, even if the feature itself is unprotected (SAS, paragraph 43).
• Graphics and sound. The Court of Justice treats them as part of the protected work (Nintendo v PC Box, paragraph 23).
• Text and manuals. Copying elements of a protected manual can infringe it (SAS, third point of the ruling). Written game rules can also be protected.
• Characters, story and world, as far as they are original expression.

Can you use a game's name?

Names are usually not a copyright question. The US Copyright Office treats names, titles and short phrases as uncopyrightable, and it adds that they may be protectable under other law.

That other law is mainly trademark law. In Germany a mark arises through registration, through use that gains recognition in the market, or through being well known (§ 4 MarkenG). The owner can act against identical signs for identical goods, and against similar signs where there is a likelihood of confusion (§ 14 MarkenG). Titles of works can be protected separately under § 5 MarkenG, and the Mannheim Regional Court accepted that game names can be such work titles. It applied a strict standard to copyright in the names themselves, which it refused.

Do not build your product, character or marketing on someone else's game name or a near copy of it.

How close can the look be?

There is no percentage. In Tetris v. Xio a US court found infringement where a user could not tell two games apart, and it stressed the wholesale copying of the look. In Spry Fox v. LOLApps a claim survived a motion to dismiss even though the art had changed from bears to yetis.

German law asks a related question. Under § 23 UrhG, adaptations of a work need consent, but a new work that keeps sufficient distance from the work it used is not an adaptation. Separately, § 4 no. 3 UWG can make it unfair to offer an imitation of a competitor's product, for example where it avoidably deceives buyers about its origin or unfairly exploits the reputation of the original. Unfair competition law can therefore apply on top of copyright, though the Mannheim court found a bare allegation of imitation insufficient.

Can you use data extracted from a game?

Treat this as the riskiest category. The law distinguishes what you can observe from what you take out.

• Decompilation. Article 6 of the Software Directive and § 69e UrhG allow it only where indispensable for interoperability of an independently created program, and only within strict limits. The information may not be used to develop a program substantially similar in its expression.
• Assets and tables from game files. Art, audio and text remain protected when they sit in a file. Numbers are not automatically free either: a collection of data can be protected by the database right where the maker shows a substantial investment in obtaining, verifying or presenting it (Article 7 of Directive 96/9/EC, § 87b UrhG). Extracting a substantial part is then restricted, and systematic extraction of small parts can be too.
• Values in working memory. In C-159/23 (17 October 2024) the Court of Justice held that the content of variable data a program places in RAM does not fall within the protection of the Software Directive, as far as it does not enable the program to be reproduced or subsequently created. That concerns the Software Directive only. It does not make extraction lawful under other rights or under contract.
• Terms of use. Article 8 voids contract terms against Article 5(3) and Article 6, not every term. A licence can still bind you in other respects.

The specs in this library follow one rule for that reason: nothing comes from ROMs, decompilations, datamined tables or leaks.

Does copying many mechanics from one game change things?

It can. Both US cases looked at the overall impression and at how much was taken together, and not only at single elements. The more of one game's selection and presentation you take, the less you can rely on arguing that each part is only an idea. This is why we do not publish breakdowns of individual games.

Does it matter if an AI agent does the copying?

Using a tool does not change what was copied. You publish the result, and you carry the risk. Agents can also reproduce names and details without being asked, so review their output. In October 2026 Anthropic confirmed that it had added text to Claude Code on Opus 5.5 to steer it away from recreating someone else's specific game, while original and genre games stay in scope, Game Developer reported.