---
name: dotnet-modern-csharp-editorconfig
description: Drop-in opinionated .editorconfig for modern C# (C# 14 on .NET 10, also works with C# 10–13) that enforces concise, readable code leveraging the latest language features. Use when setting up code-style rules, naming conventions, formatting, and preview analyzer severities for a new or existing .NET repo. Also covers the required .csproj flags (Nullable, TreatWarningsAsErrors, AnalysisLevel=preview-All, EnforceCodeStyleInBuild) and the .NET 8 vs .NET 9+ build-respect-editorconfig distinction. Generated by the `mcs-editorconfig` template.
metadata:
  author: https://github.com/VincentH-Net
  version: "1.1.1"
  framework: dotnet
  category: code-style
  sources:
    - Modern.CSharp.Templates (mcs-editorconfig)
    - github.com/VincentH-Net/Modern.CSharp.Templates/blob/main/Editorconfig.md
---

# Modern C# 14 .editorconfig

Use when setting up (or overhauling) code style, naming, formatting, and analyzer severities for a modern C# codebase — one that targets .NET 10 / C# 14, or any C# 10–13 project that wants to adopt the same modern conventions.

The output is a single `.editorconfig` dropped into the current folder, tuned to promote:

- **Conciseness** — expression-bodied members, target-typed `new()`, collection expressions `[ ]`, primary constructors, file-scoped namespaces, and other C# 12–14 idioms
- **Readability** — consistent spacing, braces, and `using` ordering
- **Latest language features** — analyzer severities flipped on for modern-idiom diagnostics

Scope covers formatting, code style, naming style, and analyzer severities — all in one file.

## 1. When to use this skill

Apply when any of the following is true:

- Starting a new .NET 10 / C# 14 repo and want an opinionated style baseline
- Adding a repo-root `.editorconfig` to an existing solution that currently has none
- Replacing an aging `.editorconfig` with one that flips on preview analyzers and modern-feature diagnostics
- Standardizing style across a multi-project solution — drop at the repo root, every project inherits
- Combining with other `mcs-*` templates that already trigger this generation (pass `-s` to skip the standalone blurb)

If the repo already has an `.editorconfig` in the target folder, do NOT edit, merge, patch, or add the template URL to the existing file. Ask the user whether to replace it with the generated Modern C# baseline. If the user says no, STOP. If the user says yes, run `dotnet new mcs-editorconfig --force` in the target folder.

## 2. Prerequisites

.NET CLI on PATH. First-time install of the template package:

```bash
dotnet new install Modern.CSharp.Templates
```

Confirm availability:

```bash
dotnet new list mcs
```

## 3. Generate the file

Run in the folder where the `.editorconfig` should live (typically repo root so every project inherits):

```bash
dotnet new mcs-editorconfig
```

Options:

| Option | Effect |
|---|---|
| `-s`, `--skipmanualinstructions` | Suppress the printed manual-setup blurb. Use when this template runs as part of another `mcs-*` template chain. |
| `--force` | Overwrite an existing `.editorconfig` in the folder. |
| `-o <dir>` | Write to a specific folder instead of the current directory. |

## 4. Required .csproj settings

The `.editorconfig` alone does not enforce style on `dotnet build`. Add this `PropertyGroup` to  `Directory.Build.props` in the same folder as `.editorconfig` so it applies in all `.csproj` files in or below that folder:

```xml
<PropertyGroup>
  <Nullable>enable</Nullable>
  <TreatWarningsAsErrors>true</TreatWarningsAsErrors>
  <AnalysisLevel>preview-All</AnalysisLevel>
  <EnforceCodeStyleInBuild>true</EnforceCodeStyleInBuild>

  <!-- GenerateDocumentationFile is true to enable IDE0005 (Remove unnecessary usings/imports) on build.
       This also enables CS1591 (Missing XML comment for publicly visible type or member);
       for projects that do not require comprehensive XML documentation,
       exclude CS1591 with the MSBuild NoWarn property to prevent XML doc slop. -->
  <GenerateDocumentationFile>true</GenerateDocumentationFile>
</PropertyGroup>
```

In ALL `.csproj` files in or below the folder where the `.editorconfig` resides, ensure that CS1591 is excluded with `NoWarn` to prevent XML doc slop. For example, to exclude CS1591:

```xml
<PropertyGroup>
  <!-- Exclude CS1591 to prevent XML doc slop if this project does not require comprehensive XML documentation.
       Do NOT set GenerateDocumentationFile to false; it is required for the 
       IDE0005 (Remove unnecessary usings/imports) analyzer to function. -->
  <NoWarn>$(NoWarn);CS1591</NoWarn>
</PropertyGroup>
```

This MUST be in `.csproj` files; it cannot be in the `Directory.Build.props` file because some projects may require comprehensive XML documentation while others do not; excluding CS1591 must be an explicit choice per project. By excluding CS1591 in all project files initially, we enable opt-in to comprehensive XML documentation on a per-project basis by removing CS1591 from that project's `NoWarn` list.

## 5. Opinionated choices worth calling out

- **No underscore prefix on private fields.** Naming rules permit `camelCase` for private instance fields and reject `_camelCase`. This is a deliberate divergence from the common underscore-prefix convention — if your repo has existing `_field` code, a repo-wide rename is implied.
- Rationale for every non-default setting is documented inline inside the generated `.editorconfig`. Read the file comments before editing, and update the comment if you change a rule.

## 6. Combining with other mcs templates

Other `mcs-*` templates may generate their own `.editorconfig` already based on this one. In particular:

- **`mcs-orleans-multiservice`** writes an **extended** `.editorconfig` at the solution root that builds on this baseline and layers Orleans-specific rules on top. **Do not** run `mcs-editorconfig` separately in that solution — the extended file is already there. See the `orleans-multiservice-pattern` skill.

When this template *is* chained into a custom project-generation flow (not superseded by another template that already includes it), suppress the standalone instructions blurb:

```bash
dotnet new mcs-editorconfig -s
```

## 7. Build diagnostic handling

Before building, check whether `AGENTS.md` or `AGENTS.MD` in the current working folder contains
`<!-- dotnet-agentic-engineering:dotnet-build-errors-and-warnings:start -->` or
`<!-- dotnet-agentic-engineering:dotnet-build-errors-and-warnings:skip -->`.
If neither marker is present, use the `ensure-directives` skill first.

Use the installed `dotnet-build-errors-and-warnings` directive for build verification and diagnostic fixes.
That directive governs when to run `dotnet format`, how to fix build errors and warnings, and when suppressions are allowed.

## 8. Verification

After generation and csproj wiring, confirm the rules take effect at build:

```bash
dotnet build
```

A clean build with no `IDE*` / `CA*` diagnostics confirms the editorconfig + csproj combination is active. If you expect diagnostics to fire and none appear, re-check `EnforceCodeStyleInBuild` and, on .NET 8, `AnalysisLevel`.

## References

- [Modern.CSharp.Templates — Editorconfig.md](https://github.com/VincentH-Net/Modern.CSharp.Templates/blob/main/Editorconfig.md)
- [NuGet: Modern.CSharp.Templates](https://www.nuget.org/packages/Modern.CSharp.Templates)