> ## Documentation Index
> Fetch the complete documentation index at: https://ancplua.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Diagnostics

> Generator diagnostics for MCP server validation.

The generator reports diagnostics at build time for invalid MCP server declarations.

## Rules

| Id     | Severity | Description                                        |
| ------ | :------: | -------------------------------------------------- |
| QA0001 |   Error  | `[McpServer]` class must be `partial`              |
| QA0002 |   Error  | `[McpServer]` class must not be `static`           |
| QA0003 |   Error  | `[McpServer]` class must not be generic            |
| QA0004 |   Error  | `[Tool]` method must be inside `[McpServer]` class |
| QA0005 |   Error  | `[Tool]` method must not be `static`               |
| QA0006 |   Error  | `[Tool]` method must not be generic                |
| QA0007 |   Error  | `[Tool]` method has unsupported return type        |
| QA0008 |   Error  | `[Tool]` parameter has unsupported type            |
| QA0009 |  Warning | `[Tool]` parameter missing `[Description]`         |
| QA0010 |  Warning | `[McpServer]` class has no `[Tool]` methods        |
| QA0011 |   Error  | Duplicate tool name in same server                 |
| QA0012 |  Warning | All tool safety hints are `Unset`                  |
| QA0013 |   Error  | `[Resource]` method has invalid return type        |
| QA0014 |   Error  | Duplicate resource URI in same server              |
| QA0015 |   Error  | `[Prompt]` method has invalid return type          |
| QA0016 |   Error  | Duplicate prompt name in same server               |

## Examples

### QA0001 — Class must be partial

```csharp theme={null}
// Bad: not partial
[McpServer]
public class MyServer { }

// Good: partial
[McpServer]
public partial class MyServer { }
```

### QA0004 — Orphaned tool

```csharp theme={null}
// Bad: no [McpServer] on containing class
public partial class NotAServer
{
    [Tool]
    public string Echo(string input) => input;
}
```

### QA0009 — Missing description

```csharp theme={null}
[McpServer]
public partial class MyServer
{
    [Tool]
    public string Echo(string input) => input;
    //                  ^ QA0009: parameter 'input' has no [Description]
}
```

Add `[Description]` to suppress:

```csharp theme={null}
[Tool]
public string Echo([Description("Text to echo")] string input) => input;
```

### QA0012 — All safety hints Unset

Only fires when all four hints are **explicitly** set to `ToolHint.Unset`:

```csharp theme={null}
// Triggers QA0012
[Tool(ReadOnly = ToolHint.Unset, Idempotent = ToolHint.Unset,
      Destructive = ToolHint.Unset, OpenWorld = ToolHint.Unset)]
public string Echo(string input) => input;

// No diagnostic — hints left at defaults
[Tool]
public string Echo(string input) => input;
```

### QA0013 — Resource invalid return type

`[Resource]` methods must return `string`, `Task<string>`, or `ValueTask<string>`.

### QA0014 — Duplicate resource URI

Two methods in the same server cannot share a `[Resource]` URI.

### QA0015 — Prompt invalid return type

`[Prompt]` methods must return `string`, `Task<string>`, `PromptResult`, or `Task<PromptResult>`.

### QA0016 — Duplicate prompt name

Two methods in the same server cannot share a `[Prompt]` name.

## Configuration

```editorconfig theme={null}
[*.cs]
dotnet_diagnostic.QA0009.severity = none
```