Bootstrapping LLM Dev Container

An opinionated, drop-in, reproducible development environment for C# / .NET projects with first-class support for AI-assisted workflows. The repository packages a ready-to-use .devcontainer configuration and a collection of homegrown skills for use with AI coding agents such as Claude Code and OpenCode.

This is a work in progress. Enjoy! Or don't — I don't care. —Robert

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What's in this repository?

.
├── devcontainer/
│   └── .devcontainer/          # Drop-in dev container configuration
├── skills/                     # Custom AI agent skills
├── DEV CONTAINER README.md     # Detailed dev container documentation
└── README.md                   # This file

.devcontainer

A fully configured development container built around modern .NET development. It provides a consistent, reproducible environment that works the same across Windows, macOS, and Linux — fewer "works on my machine" problems.

Included tooling at a glance:

Category	Tools
Runtime	.NET 10 SDK, Python, Node.js, PowerShell
AI Agents	Claude Code, OpenCode
AI Agent Plugins	csharp-lsp, pyright-lsp
Formatters	CSharpier, Prettier
Shell	Zsh, Oh My Zsh, Oh My Posh
.NET CLI Tools	dotnet-ef, dotnet-script, dotnet-trace, dotnet-counters, dotnet-dump, dotnet-outdated
Terminal utilities	ripgrep, fd, fzf, zoxide, bat, lazygit, delta, jq, tree, vim
Git	Git LFS, GitHub CLI

For full architecture details, setup steps, and troubleshooting, see DEV CONTAINER README.md.

skills/

A set of homegrown skills for AI coding agents. Skills are reusable instruction sets that guide an AI agent's behaviour for specific tasks — composable building blocks that live alongside your project. The skills in this repository are tailored to the C# / .NET development workflow the dev container supports.

Orchestration

Skill	Description
csharp-test-sweep	Systematically sweeps C# test projects one class at a time, reviewing and improving tests against quality standards. Auto-detects the test framework and mocking library from the project file and delegates to the appropriate companion skill. Supports scoped invocation by method, region, class, namespace, or full project.

Testing — Frameworks

Skill	Description
xunit-csharp	Write, update, and improve xUnit v3 unit and integration tests. Covers naming conventions, AAA structure, [Theory]/[Fact] patterns, TheoryData<T>, IXunitSerializer, Object Mother, and fixture patterns.
nunit-csharp	Write, update, and improve NUnit tests. Stub that expands with NUnit-specific patterns ([TestCase], [TestCaseSource], constraint model) on first use against an NUnit project.
mstest-csharp	Write, update, and improve MSTest tests. Stub that expands with MSTest-specific patterns ([DataTestMethod], [DataRow], [DynamicData]) on first use.

Testing — Mocking Libraries

Skill	Description
nsubstitute-csharp	Write, update, and improve NSubstitute mock setups. Covers the abstract-class interception trap, partial substitutes, argument matchers, and call verification.
moq-csharp	Write, update, and improve Moq mock setups. Stub that expands with Moq-specific patterns (MockBehavior, SetupProperty, Capture, InSequence) on first use.
justmock-csharp	Write, update, and improve Telerik JustMock mock setups. Covers free vs elevated/profiler mode, Mock.Arrange, Mock.Assert, and Behavior modes.
rhinomocks-csharp	Write, update, and improve RhinoMocks mock setups. Stub that expands with RhinoMocks AAA patterns on first use. Flags migration opportunities to NSubstitute or Moq — RhinoMocks is largely unmaintained.

Documentation

Skill	Description
gen-dotnet-docs-comments	Add and improve XML documentation comments (///) and inline comments (//) in C# codebases. Scoped by type, member, or namespace. Writes for senior developer consumers — context, constraints, and domain concepts, not narrative repetition of signatures.
reverse-engineered-docs	Reverse-engineers an existing project from source code and produces structured markdown documentation: project overview, DDD domain breakdown, and per-feature docs. Supports interactive and batch modes.

Refactoring

Skill	Description
split-type-to-partials	Refactors a C# type into partial files split by implemented interface and functional grouping (Factory, Operators). Mirrors the split in the corresponding test file and updates the .csproj with DependentUpon nesting.

Note on stubs: Several mocking and framework skills (moq-csharp, mstest-csharp, nunit-csharp, rhinomocks-csharp) ship as stubs. They contain universal rules pre-applied to the library's API but expand automatically with library-specific patterns the first time csharp-test-sweep runs against a project using that library.

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Prerequisites

• Docker Desktop (Windows / macOS) or Docker Engine (Linux)
• Visual Studio Code with the Dev Containers extension
  • Other dev container hosts may work, but this was built with VS Code in mind — your mileage may vary

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Quick Start

1. Copy the dev container into your project

Copy the devcontainer/.devcontainer folder into the root of your project:

your-project/
└── .devcontainer/      ← drop this folder here
    ├── devcontainer.json
    ├── Dockerfile
    ├── docker-compose.yml
    ├── docker-compose.local.example.yml
    ├── post-create.sh
    ├── post-start.sh
    └── dotfiles/

2. Create your local override file

The container uses a gitignored local compose override for personal host paths. Copy the example template:

cp .devcontainer/docker-compose.local.example.yml .devcontainer/docker-compose.local.yml

Do not commit this file. It holds personal paths and is already listed in .devcontainer/.gitignore.

3. Set the required environment variables

The local override references three host directories. Set them as persistent user-level variables so VS Code picks them up.

Windows (PowerShell):

[System.Environment]::SetEnvironmentVariable("CLAUDE_DIR",     "$HOME\.claude",    "User")
[System.Environment]::SetEnvironmentVariable("GITCONFIG_PATH", "$HOME\.gitconfig",  "User")
[System.Environment]::SetEnvironmentVariable("SSH_DIR",        "$HOME\.ssh",        "User")

Linux / macOS — add to ~/.bashrc or ~/.zshrc:

export CLAUDE_DIR="$HOME/.claude"
export GITCONFIG_PATH="$HOME/.gitconfig"
export SSH_DIR="$HOME/.ssh"

Alternatively, create a .devcontainer/.env file (also gitignored) to avoid a shell restart:

CLAUDE_DIR=C:\Users\YourName\.claude
GITCONFIG_PATH=C:\Users\YourName\.gitconfig
SSH_DIR=C:\Users\YourName\.ssh

4. Open in VS Code

Open your project in VS Code. When prompted, select Reopen in Container — or run from the Command Palette (Ctrl+Shift+P):

Dev Containers: Rebuild and Reopen in Container

The container will build, run the post-create script, and land you in a fully configured environment.

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Design Philosophy

Reproducibility. All shared tooling is defined once in the container image and inherited by every developer on the project. Nothing to install manually.

Portability. Personal configuration — AI agent state, SSH keys, git identity — is supplied at runtime through bind mounts and never baked into the image. The repository stays clean.

Persistence. NuGet packages and Claude Code configuration survive container rebuilds via named Docker volumes and host bind mounts. Skills, memory, and agent state persist across rebuilds.

AI-first. The environment is designed for AI-assisted workflows. Two agents (Claude Code and OpenCode) are pre-configured with LSP diagnostics, marketplace plugins, and a library of C# skills ready to use on first launch.

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Further Reading

• DEV CONTAINER README.md — full architecture reference, per-platform setup, persistent storage, and troubleshooting
• Dev Containers specification — upstream documentation for the .devcontainer format
• Claude Code documentation — documentation for Claude Code
• OpenCode documentation — documentation for OpenCode