ManagedCode.CodexSharpSDK

ManagedCode.CodexSharpSDK is an open-source .NET SDK for driving the Codex CLI from C#.

It is a CLI-first .NET 10 / C# 14 SDK aligned with real codex runtime behavior, with:

• thread-based API (start / resume)
• streamed JSONL events
• structured output schema support
• image attachments
• --config flattening to TOML
• NativeAOT-friendly implementation and tests on TUnit

All consumer usage examples are documented in this README; this repository intentionally does not keep standalone sample projects.

Installation

dotnet add package ManagedCode.CodexSharpSDK

Prerequisites

Before using this SDK, you must have:

• codex CLI installed and available in PATH
• an already authenticated Codex session (codex login)

Quick check:

codex --version
codex login

Quickstart

using ManagedCode.CodexSharpSDK;

using var client = new CodexClient();

var thread = client.StartThread(new ThreadOptions
{
    Model = CodexModels.Gpt53Codex,
    ModelReasoningEffort = ModelReasoningEffort.Medium,
});

var turn = await thread.RunAsync("Diagnose failing tests and propose a fix");

Console.WriteLine(turn.FinalResponse);
Console.WriteLine($"Items: {turn.Items.Count}");

AutoStart is enabled by default, so StartThread() works immediately.

Advanced Configuration (Optional)

using var client = new CodexClient(new CodexClientOptions
{
    CodexOptions = new CodexOptions
    {
        // Override only when `codex` is not discoverable via npm/PATH.
        CodexExecutablePath = "/custom/path/to/codex",
    },
});

var thread = client.StartThread(new ThreadOptions
{
    Model = CodexModels.Gpt53Codex,
    ModelReasoningEffort = ModelReasoningEffort.High,
    SandboxMode = SandboxMode.WorkspaceWrite,
});

Extended CLI Options

ThreadOptions supports full codex exec control.

var thread = client.StartThread(new ThreadOptions
{
    Profile = "strict",
    UseOss = true,
    LocalProvider = OssProvider.LmStudio,
    FullAuto = true,
    Ephemeral = true,
    Color = ExecOutputColor.Auto,
    EnabledFeatures = ["multi_agent"],
    DisabledFeatures = ["steer"],
    AdditionalCliArguments = ["--some-future-flag", "custom-value"],
});

Codex CLI Metadata

using var client = new CodexClient();

var metadata = client.GetCliMetadata();
Console.WriteLine($"Installed codex-cli: {metadata.InstalledVersion}");
Console.WriteLine($"Default model: {metadata.DefaultModel ?? "(not set)"}");

foreach (var model in metadata.Models.Where(model => model.IsListed))
{
    Console.WriteLine(model.Slug);
}

GetCliMetadata() reads:

• installed CLI version from codex --version
• default model from ~/.codex/config.toml
• model catalog from ~/.codex/models_cache.json

var update = client.GetCliUpdateStatus();
if (update.IsUpdateAvailable)
{
    Console.WriteLine(update.UpdateMessage);
    Console.WriteLine(update.UpdateCommand);
}

GetCliUpdateStatus() compares installed CLI version with latest published @openai/codex npm version and returns an update command matched to your install context (bun or npm).

When thread-level web search options are omitted, SDK does not emit a web_search override and leaves your existing CLI/config value as-is.

Client Lifecycle and Thread Safety

• CodexClient is safe for concurrent use from multiple threads.
• StartAsync() is idempotent and guarded.
• StopAsync() cleanly disconnects client state.
• Dispose() transitions client to Disposed.
• A single CodexThread instance serializes turns (RunAsync and RunStreamedAsync) to prevent race conditions in shared conversation state.

Streaming

var streamed = await thread.RunStreamedAsync("Implement the fix");

await foreach (var evt in streamed.Events)
{
    switch (evt)
    {
        case ItemCompletedEvent completed:
            Console.WriteLine($"Item: {completed.Item.Type}");
            break;
        case TurnCompletedEvent done:
            Console.WriteLine($"Output tokens: {done.Usage.OutputTokens}");
            break;
    }
}

Structured Output

using System.Text.Json.Serialization;

public sealed record RepositorySummary(string Summary, string Status);

[JsonSerializable(typeof(RepositorySummary))]
internal sealed partial class AppJsonContext : JsonSerializerContext;

var schema = StructuredOutputSchema.Map<RepositorySummary>(
    additionalProperties: false,
    (response => response.Summary, StructuredOutputSchema.PlainText()),
    (response => response.Status, StructuredOutputSchema.PlainText()));

var result = await thread.RunAsync<RepositorySummary>(
    "Summarize repository status",
    schema,
    AppJsonContext.Default.RepositorySummary);
Console.WriteLine(result.TypedResponse.Status);
Console.WriteLine(result.TypedResponse.Summary);

For advanced options (for example cancellation), use the TurnOptions overload:

using var cancellation = new CancellationTokenSource(TimeSpan.FromSeconds(30));

var result = await thread.RunAsync<RepositorySummary>(
    "Summarize repository status",
    AppJsonContext.Default.RepositorySummary,
    new TurnOptions
    {
        OutputSchema = schema,
        CancellationToken = cancellation.Token,
    });

RunAsync<TResponse> always requires OutputSchema (direct parameter or TurnOptions.OutputSchema). For AOT/trimming-safe typed deserialization, pass JsonTypeInfo<TResponse> from a source-generated context. Overloads without JsonTypeInfo<TResponse> are explicitly marked with RequiresDynamicCode and RequiresUnreferencedCode.

Diagnostics Logging (Optional)

using Microsoft.Extensions.Logging;

public sealed class ConsoleCodexLogger : ILogger
{
    public IDisposable BeginScope<TState>(TState state)
        where TState : notnull
    {
        return NullScope.Instance;
    }

    public bool IsEnabled(LogLevel logLevel)
    {
        return true;
    }

    public void Log<TState>(
        LogLevel logLevel,
        EventId eventId,
        TState state,
        Exception? exception,
        Func<TState, Exception?, string> formatter)
    {
        Console.WriteLine($"[{logLevel}] {formatter(state, exception)}");
        if (exception is not null)
        {
            Console.WriteLine(exception);
        }
    }

    private sealed class NullScope : IDisposable
    {
        public static NullScope Instance { get; } = new();
        public void Dispose() { }
    }
}

using var client = new CodexClient(new CodexOptions
{
    Logger = new ConsoleCodexLogger(),
});

Images + Text Input

using var imageStream = File.OpenRead("./photo.png");

var result = await thread.RunAsync(
[
    new TextInput("Describe these images"),
    new LocalImageInput("./ui.png"),
    new LocalImageInput(new FileInfo("./diagram.jpg")),
    new LocalImageInput(imageStream, "photo.png"),
]);

Resume an Existing CodexThread

var resumed = client.ResumeThread("thread_123");
await resumed.RunAsync("Continue from previous plan");

Build and Test

dotnet build ManagedCode.CodexSharpSDK.slnx -c Release -warnaserror
dotnet test --solution ManagedCode.CodexSharpSDK.slnx -c Release