If you've spent any time on dev Twitter, LinkedIn, or your team's Slack channel lately, you've probably heard developers talking about Claude Code . Most of that talk comes from the Python and JavaScript crowd. But it works just as well in a .NET project — and once you've tried it on a real C# codebase, it's hard to go back to copy-pasting code into a chat window.
This article walks through what Claude Code actually is, how to set it up next to your existing .NET tools, and — most importantly — what it looks like to use it on day-to-day C# work: writing tests, fixing bugs, refactoring Entity Framework queries, and shipping pull requests.
What Claude Code Actually Is
Most developers' first experience with AI coding tools is copy-pasting a function into a chat window, copying the answer back, and hoping it compiles. Claude Code skips that loop entirely.
Claude Code is an agentic coding tool from Anthropic. Instead of just answering questions about code you paste in, it works inside your project: it reads your files, runs your build and test commands, edits multiple files in one pass, and even manages git for you — commits, branches, and pull requests included. You describe what you want in plain English, and it plans the work, makes the changes, and verifies they actually work before handing control back to you.
For a .NET developer, the practical difference is this: instead of asking "how do I fix this NullReferenceException?" and manually applying the fix, you can say "fix this NullReferenceException, then run the tests" — and Claude Code will trace the bug through your actual codebase, make the change, and run dotnet test to confirm it worked.
Where It Fits Into a .NET Workflow
Claude Code isn't tied to one editor. It currently runs in:
The terminal — a full CLI, works with any project regardless of IDE
VS Code — an extension with inline diffs and a chat panel right in the editor
JetBrains IDEs — including Rider, which a lot of .NET teams already use
A desktop app — for reviewing diffs visually and running sessions outside an IDE
The browser — for kicking off longer tasks without a local setup
One honest caveat worth knowing: there isn't (yet) a dedicated extension for classic Visual Studio, which is still the default IDE for a large chunk of the .NET world. The common pattern right now is to keep Visual Studio open for the parts of your workflow that work best there (designers, debugging, NuGet management) and run Claude Code in a terminal alongside it, or switch to VS Code/Rider when you want the inline diff experience. Either way, your project files, settings, and instructions carry over — Claude Code isn't locked to a single editor.
Getting Started
Installing the CLI is a one-line command. On macOS, Linux, or WSL:
bash
curl -fsSL https://claude.ai/install.sh | bash
On Windows (PowerShell):
powershell
irm https://claude.ai/install.ps1 | iex
Once it's installed, navigate to your .NET solution and start a session:
bash
cd MyDotNetApp
claude
You'll sign in with a Claude account on first run, and from there you're working directly against your project.
Example 1: Writing Tests for Untested Code
Say you've got an OrderService class with business logic that's never had test coverage — a common situation in older .NET codebases. Instead of writing the test scaffolding by hand, you can just ask:
bash
claude "write xUnit tests for OrderService, covering the discount and tax calculation methods, then run them and fix any failures"
Claude Code will open OrderService.cs, look at how the class is actually used elsewhere in your solution (so it gets constructor dependencies and mocking right), generate the test file, run dotnet test, and iterate if anything fails — all without you touching the keyboard in between.
Example 2: Fixing a Bug From a Stack Trace
This is one of the most common real-world uses. Paste the exception straight from your logs:
bash
claude "I'm getting this exception when placing an order:
System.NullReferenceException: Object reference not set to an instance of an object.
at MyApp.Services.OrderService.CalculateTotal(Order order) in OrderService.cs:line 42
Find the cause and fix it."
Claude Code traces the call path, looks at where Order objects get constructed, identifies the missing null check (or the upstream method that's failing to populate a field), and applies a fix — then tells you what it changed and why.
Example 3: Cleaning Up an EF Core Query
Entity Framework Core is a frequent source of subtle performance issues, especially N+1 query problems that aren't obvious until you check the SQL being generated. You can point Claude Code straight at the problem:
bash
claude "Review the GetCustomerOrders method in CustomerRepository.cs for any N+1 query issues with EF Core, and rewrite it using Include or projection as appropriate"
It will read the method, recognize the lazy-loading pattern that's causing repeated round trips, and rewrite it with proper eager loading or a projected query — explaining the reasoning in plain language so you're not just trusting a black box.
Example 4: Git Without Leaving the Terminal
Claude Code talks to git directly, so the usual end-of-task chores disappear:
bash
claude "commit my changes with a descriptive message"
claude "open a pull request for this branch summarizing the changes I made to the authentication module"
It writes the commit message based on the actual diff, not a generic placeholder, and the same applies to PR descriptions.
The four examples above are what most teams try first. The two below are harder — the kind of bug that takes an experienced engineer real time to track down.
Example 5: Hunting Down a Sync-over-Async Deadlock
This is a classic ASP.NET problem that's painful precisely because it's intermittent. Everything works fine locally, then a production endpoint hangs under real traffic and only recovers after a timeout. The usual culprit: somewhere in the call chain, an async method is being called with .Result or .Wait() instead of await, exhausting the thread pool or deadlocking against a captured synchronization context.
bash
claude "Our checkout endpoint hangs under load and only recovers after a 30-second timeout.
Trace the call chain from the controller through OrderService and PaymentGateway,
find any blocking calls on async code, and fix the deadlock properly —
not by sprinkling ConfigureAwait(false) everywhere, but by making the call chain async end-to-end."
What makes this difficult isn't writing the fix — it's the diagnosis. Claude Code has to read across several files, recognize the specific anti-pattern (a stray .Result, .Wait(), or a Task.Run wrapper hiding a deeper issue), and trace it from the controller all the way down through the service and gateway layers. A surface-level fix here is sprinkling ConfigureAwait(false) everywhere and hoping it helps; a real fix makes the chain properly asynchronous end-to-end and explains why the deadlock was happening — the kind of reasoning you'd want from a senior engineer doing the same code review.
Example 6: Catching a Cross-Tenant Data Leak Before It Ships
If you're building a multi-tenant SaaS product, this is the bug that keeps people up at night: one tenant's data showing up in another tenant's account. These leaks tend to hide in places a quick review skims past — a raw SQL query missing its TenantId predicate, an IgnoreQueryFilters() call left over from debugging, or an Include() pulling in related data without the same filter applied.
bash
claude "We had a report of one tenant seeing another tenant's invoices. Before changing anything,
search the entire data access layer for anywhere our TenantId filtering could be bypassed —
raw SQL, IgnoreQueryFilters, manually constructed queries, cached data —
and give me a report of every place you find, ranked by how likely it is to be the cause."
Notice the prompt asks for a report before any code changes — that's deliberate, and it's good practice for any security-sensitive bug. Claude Code can search an entire solution far faster than a manual grep-and-read pass, but for a bug with real customer-trust implications, you want a ranked list of suspects and reasoning to review, not an autonomous fix applied on the first guess.
Setting Project-Wide Conventions With CLAUDE.md
This is the feature that makes the biggest difference once you start using Claude Code regularly. Drop a CLAUDE.md file in your project root, and Claude Code reads it at the start of every session — so you only have to state your team's conventions once:
# CLAUDE.md
- Target framework: .NET 9
- Use nullable reference types everywhere; no suppressing warnings with `!` unless justified in a comment
- Prefer `record` types for DTOs
- All public methods need XML doc comments
- Use EF Core's `AsNoTracking()` for read-only queries
- Run `dotnet test` before considering any task complete
- Follow the existing repository pattern in `/Data/Repositories`
From that point on, every fix, feature, and refactor Claude Code does for that project follows these rules automatically — no need to repeat them in every prompt.
A Few Practical Tips
Start small. Point it at one bug or one missing test file before trusting it with a multi-file feature.
Review the diff. Claude Code shows you what changed before committing — treat it like reviewing a junior developer's PR.
Use plan mode for bigger changes. Ask it to lay out its approach first so you can correct direction before code gets written.
Let it run your test suite. The more it can verify its own work with dotnet test or dotnet build, the less manual checking you'll need afterward
Summary
Claude Code isn't a replacement for understanding your own codebase — it's closer to a fast, literal-minded pair programmer who never tires of writing tests or chasing a stack trace. For .NET teams, the combination of git integration, project-wide conventions via CLAUDE.md, and the ability to verify its own work with dotnet test and dotnet build is what separates it from "AI chat with code highlighting."
If you haven't tried it yet, start small: point it at one untested class, or one bug from your error logs, and see how it handles your actual code — not a toy example.