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.cursor/rules/project.mdc

Cursor rules for Unreal

Cursor rules are a markdown file with a short frontmatter header. Cursor attaches them to the agent so it stops guessing how this repo builds, tests, and styles code. This copy is written for a Unreal project. This repository is an Unreal Engine project using C++. UObject memory is owned by the engine. Gameplay stays out of constructors that run before the world exists.

The example uses a balanced, readable style, pragmatic tests, and comments only where the intent is not obvious. Open the generator to make the agent stricter, switch to test-first, quiet the comments, or pick a different file.

The example assumes Unreal Engine with C++ gameplay code. It does not assume a particular networking model, Enhanced Input, or GAS unless the module already uses them.

Customize in the generatorBrowse the library

Example file

Balanced strictness, readable style, pragmatic tests. Download name: project.mdc. Legacy path: .cursorrules

---
description: "Working rules for a Unreal repository"
globs: "**/*"
alwaysApply: true
---

# Project rules

Follow these rules on every task in this Unreal repository.
If the project still uses a root `.cursorrules` file, keep the same rules there.

## Stack

This repository is an Unreal Engine project using C++. UObject memory is owned by the engine. Gameplay stays out of constructors that run before the world exists.

## Layout

- Runtime code lives in the game module. Editor-only code lives in an editor module.
- Generated headers stay included last, the way the module already does.
- Blueprints are data. Do not hard-code tuning that a designer already edits.

## Commands

- Build: `Build the editor target for this project`
- Tests: `Run the Unreal automation tests for the module you changed`

Use the script the repo already defines when it differs from the command above.

## Conventions

- Mark reflected fields with UPROPERTY and the specifiers the class already uses.
- Do not `new` a UObject. Use `NewObject`, `CreateDefaultSubobject`, or `SpawnActor`.
- Do not tick a component that only needs to react to an event.
- Keep gameplay off the garbage-collected raw pointer across a frame without a UPROPERTY or TWeakObjectPtr.
- Name types with the project's prefix if it has one.
- Hot-reload limitations are real. A header change may need a full rebuild.

## Testing

Add or update tests when behavior changes.

Add an Unreal automation test when the rule is pure C++. Otherwise say which PIE case you ran.

## Style

- Optimize for the next reader over the shortest diff.
- Comment only when the why is non-obvious.
- Name things the way neighboring files already do.
- Do not reformat code you did not change.

## Errors

- Fail at the boundary. Do not swallow errors.
- Use `ensure` or a logged early return for a missing asset. Do not check() on data a content change can break.

## Scope

- Do the requested task. Do not refactor unrelated code.
- Match the rigor already in the repo. Fix what you touch.
- Ask one clarifying question only when the task cannot be finished without it. Otherwise state the assumption and continue.

## Avoid

- Do not call into UObjects from a worker thread.
- Do not store a raw UObject pointer in a non-reflected struct and expect it to stay alive.
- Do not edit generated files under Intermediate.
- Do not commit Binaries, DerivedDataCache, or Saved unless the project already vendors a specific binary.

## Done when

- The requested behavior works.
- The editor target compiles and the automation test or PIE session for the change was run.
- The diff stays inside the task.
- You list anything you could not run.

Add it to the project

  1. 01

    Copy a starting file

    Copy the example Cursor rules on this page, or open the generator if you want different testing, strictness, or comment rules.

  2. 02

    Save it at .cursor/rules/project.mdc

    Save it at `.cursor/rules/project.mdc` in the Unreal repo and create the folders if they are missing. If the project still uses one root rules file, save the body as `.cursorrules`.

  3. 03

    Start a fresh agent session

    Rules files are read when a session starts. A chat that is already open may still be using the old instructions.

  4. 04

    Give it one small task

    Ask for one change a Unreal agent often gets wrong, such as a UPROPERTY that is visible to the editor without a raw new of a UObject. If it ignores the file, confirm the path and start a new session.

Questions about this file

Where do I put Cursor rules in a Unreal repo?

Save it at `.cursor/rules/project.mdc` in the Unreal repo and create the folders if they are missing. If the project still uses one root rules file, save the body as `.cursorrules`.

Which tools read this Cursor rules?

Cursor reads `.cursor/rules/*.mdc` and, on older setups, a root `.cursorrules` file. Other tools ignore the frontmatter, so use AGENTS.md when more than one agent edits the repo.

What does the Unreal example assume?

The example assumes Unreal Engine with C++ gameplay code. It does not assume a particular networking model, Enhanced Input, or GAS unless the module already uses them.

Does VibeSpell upload my repository?

No. Recipe pages are static, and the generator builds the file in your browser from the options you pick. Your source code never leaves the machine.

Other files for Unreal

Cursor rules for other stacks