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.cursor/rules/project.mdc

Cursor rules for .NET

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 .NET project. This repository is a .NET application. Nullable reference types stay enabled. Match minimal APIs or controllers, whichever the project already uses, and ship schema changes as migrations.

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 modern .NET with nullable enabled. It does not assume MVC versus minimal APIs, or EF Core versus another store. Follow the host that is already in Program.cs.

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 .NET repository"
globs: "**/*"
alwaysApply: true
---

# Project rules

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

## Stack

This repository is a .NET application. Nullable reference types stay enabled. Match minimal APIs or controllers, whichever the project already uses, and ship schema changes as migrations.

## Layout

- Endpoints or controllers stay next to the feature folder the repo uses.
- EF Core DbContext and configurations stay in the data project if there is one.
- Do not add a second hosting model.

## Commands

- Test: `dotnet test`
- Run: `dotnet run`
- Format: `dotnet format`

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

## Conventions

- Respect nullable annotations. Do not silence them with `!` unless the value was just checked.
- Validate input with the project's data annotations or fluent validation.
- Use async all the way. Do not block on `.Result`.
- Migrations ship with model changes. Do not hand-edit a snapshot to hide a mistake.
- Inject dependencies through the constructor. Do not service-locate in a loop.
- Log with ILogger. Do not use Console.WriteLine for request failures.

## Testing

Add or update tests when behavior changes.

Add an xUnit, NUnit, or MSTest test matching the repo. Cover the validation failure.

## 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.
- Return a ProblemDetails or the project's error type for expected failures. Unexpected exceptions hit the exception handler.

## 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 catch Exception and return Ok.
- Do not use dynamic to dodge a type.
- Do not query inside a serializer loop. Shape the response in the handler.
- Do not store secrets in appsettings that are committed.

## Done when

- The requested behavior works.
- `dotnet test` passes and `dotnet format` leaves the diff clean.
- 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 .NET 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 .NET agent often gets wrong, such as an endpoint that returns a validation problem for a bad body instead of throwing. 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 .NET repo?

Save it at `.cursor/rules/project.mdc` in the .NET 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 .NET example assume?

The example assumes modern .NET with nullable enabled. It does not assume MVC versus minimal APIs, or EF Core versus another store. Follow the host that is already in Program.cs.

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 .NET

Cursor rules for other stacks