Customization

Generated SDKs are designed for extension. All clients and models are partial classes — you can add functionality without modifying generated code.

Partial Class Extensions

Place extension files alongside (not inside) the Generated/ directory:

src/libs/MyApi/
├── Generated/              # Auto-generated — never edit
│   ├── MyApiClient.g.cs
│   └── ...
├── MyApiClient.Auth.cs     # Custom auth logic
├── MyApiClient.Helpers.cs  # Convenience methods
└── Extensions/
    └── ResponseExtensions.cs

Example extension:

namespace MyCompany.MyApi;

public partial class MyApiClient
{
    public async Task<Pet> GetPetByNameAsync(
        string name,
        CancellationToken cancellationToken = default)
    {
        var pets = await FindPetsByStatusAsync(
            status: FindPetsByStatusStatus.Available,
            cancellationToken: cancellationToken);

        return pets.First(p => p.Name == name);
    }
}

Client Hooks

Generated clients expose four partial method hooks for intercepting the HTTP pipeline:

`PrepareArguments`

Modify parameters before the request is built:

partial void PrepareArguments(HttpClient client, ref string petId)
{
    petId = petId.Trim();
}

`PrepareRequest`

Modify the HttpRequestMessage before it's sent:

partial void PrepareRequest(HttpClient client, HttpRequestMessage request,
    string url)
{
    request.Headers.Add("X-Custom-Header", "value");
}

`ProcessResponse`

Inspect or modify the HttpResponseMessage:

partial void ProcessResponse(HttpClient client,
    HttpResponseMessage response)
{
    if (response.StatusCode == HttpStatusCode.TooManyRequests)
    {
        // Log rate limit hit
    }
}

`ProcessResponseContent`

Inspect or modify the response body string:

partial void ProcessResponseContent(HttpClient client,
    HttpResponseMessage response, ref string content)
{
    // Log response for debugging
    Console.WriteLine(content);
}

Custom Auth

Override the Authorized partial method for non-standard auth:

public partial class MyApiClient
{
    partial void Authorized(HttpRequestMessage request)
    {
        request.Headers.Authorization =
            new AuthenticationHeaderValue("Token", _apiKey);
    }
}

Adding Serializable Types

For NativeAOT/trimming, register custom types with the JSON serializer context:

// JsonSerializerContextTypes.AdditionalTypes.cs
namespace MyCompany.MyApi;

public partial class JsonSerializerContextTypes
{
    public MyCustomType? CustomType { get; set; }
}

CSharpToJsonSchema Integration

SDKs that support function/tool calling use CSharpToJsonSchema:

[GenerateJsonSchema]
public interface IWeatherTools
{
    [Description("Get the current weather for a location")]
    public string GetWeather(
        [Description("City name")] string city,
        [Description("Temperature unit")] string unit = "celsius");
}

// Convert to API tools
var service = new WeatherToolsService();
var tools = service.AsTools();
var calls = service.AsCalls();

Inline Spec Patching

Common patterns for fixing specs in generate.sh:

# Remove problematic operations
cat spec.json | jq 'del(.paths["/internal/debug"])' > patched.json

# Rename a schema
cat spec.json | jq '
  .components.schemas.NewName = .components.schemas.OldName |
  del(.components.schemas.OldName)
' > patched.json

# Inject server URL
cat spec.json | jq '.servers = [{"url": "https://api.example.com"}]' > patched.json

Customization

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