Cursor Agent .NET: Practical Setup and Working Guide

Cursor Agent is a terminal-based coding agent that works well on .NET codebases when you start it with cursor-agent inside the solution folder. It reads project instructions from AGENTS.md or .cursor/rules, executes dotnet CLI commands, and edits source files. This guide covers a practical setup, a repeatable working loop, and the .NET-specific pitfalls to watch.

Cursor Agent in a .NET solution: real commands, real output

Cursor Agent fits .NET work because it is not a chat-only assistant; it reads the solution, executes shell commands, and edits files directly. In a typical .NET repo it can run dotnet build, dotnet test, dotnet format, and dotnet ef commands, then adjust code based on compiler or test output. That means you can hand it a compiler error or a failing test and it can trace the cause through the actual project files. It handles cross-file refactors such as renaming a service interface, adding a new endpoint, or moving business logic into a separate project better than a file-scoped assistant. Because it works in the terminal, it also respects SDK pinning, global.json, NuGet.config, and solution filters as long as those are described in the instructions.

The AGENTS.md file that makes dotnet work predictable

Start by running cursor-agent in the repository root, then provide a concise AGENTS.md at the repo root or rules under .cursor/rules. For .NET, the instruction file should name the solution, build/test/format commands, folder conventions, and rules the agent must follow when touching csproj files or Entity Framework Core. A general CLI setup is covered in How to use Cursor CLI: a step-by-step guide. A minimal but useful AGENTS.md:

# AGENTS.md
## Build and test
- Solution: src/MyShop.sln
- Build: dotnet build src/MyShop.sln
- Test: dotnet test src/MyShop.sln --no-restore
- Format: dotnet format src/MyShop.sln --verify-no-changes

## Project layout
- src/MyShop.Api         ASP.NET Core web API
- src/MyShop.Application Application services and DTOs
- src/MyShop.Infrastructure EF Core, repositories
- tests/MyShop.Tests     xUnit tests

## Rules for .NET work
- Enable nullable reference types in all new files.
- Use async/await for I/O; do not use .Result or .Wait.
- Keep EF Core DbContext usage inside Infrastructure; do not expose IQueryable from repositories.
- Do not edit generated migration files; run `dotnet ef migrations add <Name>` and `dotnet ef database update` only when asked.
- Prefer constructor injection; register services in Program.cs or an extension method.
- Do not change TargetFramework, PackageReference versions, or global.json without asking.

These files also help the agent find its way without extra prompts:

Keep this file short and update it when the agent repeats a mistake. For example, add a rule after it uses .Result or .Wait once. You can also put task-specific rules in .cursor/rules; they are loaded alongside AGENTS.md. The goal is to make the default behavior safe enough that you only review the diff, not every keystroke. If you work on a large solution, also mention which projects are test projects and which are shipping code, so the agent doesn’t add production dependencies to test projects.

A tight loop: one edit, one build, one test run, one diff

The most reliable loop is plan, make one small change, run minimal verification, review the diff. Commit or stash a clean state before asking for a multi-file change so the agent can see a clean git diff. Tell the agent not to restructure unrelated code. Start each task with a clear scope and acceptance criteria. After each step, force it to run the exact commands from AGENTS.md. After each step, run git diff --stat and skim the changed files; a good agent change should touch only the projects you expected.

Example prompts for typical .NET tasks:

• “Add a GET /orders endpoint to OrdersController. It should accept a customerId query parameter and return a list of order summaries from the database using the existing IOrderRepository. Add a corresponding xUnit test for the happy path.”
• “Introduce an IEmailSender service with an SMTP implementation. Register it in Program.cs using the configuration section Smtp. Do not send real email in tests; use a fake implementation.”
• “Split the 300-line ProductService into smaller query and command classes without changing behavior. Keep public method signatures intact and run all tests.”
• “Find all EF Core queries that call ToList() before filtering; rewrite them to filter in the database where possible, and add AsNoTracking for read-only queries.”
• “Update the CreateOrder handler to validate the customer credit limit before saving. Add a unit test for the validation failure case and ensure dotnet test passes.”

Where the agent shines in C# and where to keep the reins

Cursor Agent handles repetitive C# well: adding endpoints, DTO mapping, unit tests, dependency injection wiring, simple EF Core queries, and modernizing syntax. It is less reliable when it must infer migration intent, choose NuGet package versions, or refactor async code across many callers. Watch these .NET-specific areas closely:

• EF Core migrations: the agent may hand-edit generated migration classes or add columns before updating the model. Require it to run dotnet ef migrations add <Name> and review the generated snapshot and model changes.
• Async/await: it may introduce sync-over-async (.Result, .Wait) or forget await; compiler warnings and analyzers catch much of it, but review hot paths manually.
• DI lifetimes: it can register a scoped service in a singleton or capture scoped dependencies in background workers. Ask it to explain lifetime choices when wiring new services.
• csproj and NuGet: it may change package versions or add unknown packages. Ask for the exact dotnet add package command and a diff of the csproj before running anything.
• Solution structure: it may create files in the wrong project or break project references. Review git diff by project and keep the folder map from AGENTS.md visible.

Verification: dotnet build, filtered tests, and formatting

Always have the agent run tests after each change. Use the exact test command from AGENTS.md and ask for a summary of failed tests, not just a green check. Run dotnet build before tests to catch compile errors early. For xUnit, dotnet test src/MyShop.sln --filter "FullyQualifiedName~OrderTests" lets it run a single test class while iterating. For NUnit, keep the framework-specific filter command in the instructions. Require the agent to add or update tests for behavior changes, and never accept a change that deletes a failing test instead of fixing the implementation. When a test fails, prompt: dotnet test returned two failures; show the relevant test output and fix only those failures. Before merging, run the full suite once and ask the agent to format any changed files with dotnet format.

Parallel agents on one solution with AgentVera

AgentVera is a desktop app that runs Cursor Agent and other terminal coding agents in one window. For .NET work, the especially useful features are parallel agents in separate git worktrees, automatic code review after each agent turn, one-click checkpoints, and token budgets. Separate worktrees prevent two agents from fighting over the same solution file or project references, while code review catches broken builds and DI mistakes before you merge. Checkpoints make it safe to let an agent attempt a risky EF Core migration, because you can undo the whole turn. Token budgets keep long refactors from exhausting your daily usage.

Wrap-up: boring loops and green tests

Cursor Agent becomes a solid .NET teammate when you give it a narrow scope, explicit commands, and a fast verification loop. Start with AGENTS.md, keep changes small, run dotnet build and tests after each step, and treat EF Core migrations and csproj files as review points. Over time, the instructions file can grow with your own conventions.