# Csharp

> Use the official Anthropic C# SDK to send messages, stream responses, and define tools with JSON schema.

- Skill: `jorcan/csharp` (Agent Skill, multi-file: 3 files)
- Install (CLI): `npx skillmds@latest add jorcan/csharp`
- Raw SKILL.md: https://api.skillmd.com/api/skills/jorcan/csharp/raw
- Safety review: PASS (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Integrations & APIs, Coding & Dev Tools, REST & GraphQL APIs
- Tags: Anthropic, Csharp, Dotnet, Messages Api, Sdk, Streaming, Tool Use
- Author: jorcan (https://skillmd.com/u/jorcan)
- Updated: 2026-08-22
- Page: https://skillmd.com/skills/jorcan/csharp

---

# Claude API — C#

> **Note:** The C# SDK is the official Anthropic SDK for C#. Tool use is supported via the Messages API. A class-annotation-based tool runner is not available; use raw tool definitions with JSON schema. The SDK also supports Microsoft.Extensions.AI IChatClient integration with function invocation.

## Installation

```bash
dotnet add package Anthropic
```

## Client Initialization

```csharp
using Anthropic;

// Default (uses ANTHROPIC_API_KEY env var)
AnthropicClient client = new();

// Explicit API key (use environment variables — never hardcode keys)
AnthropicClient client = new() {
    ApiKey = Environment.GetEnvironmentVariable("ANTHROPIC_API_KEY")
};
```

---

## Basic Message Request

```csharp
using Anthropic.Models.Messages;

var parameters = new MessageCreateParams
{
    Model = Model.ClaudeOpus4_6,
    MaxTokens = 1024,
    Messages = [new() { Role = Role.User, Content = "What is the capital of France?" }]
};
var message = await client.Messages.Create(parameters);
Console.WriteLine(message);
```

---

## Streaming

```csharp
using Anthropic.Models.Messages;

var parameters = new MessageCreateParams
{
    Model = Model.ClaudeOpus4_6,
    MaxTokens = 1024,
    Messages = [new() { Role = Role.User, Content = "Write a haiku" }]
};

await foreach (RawMessageStreamEvent streamEvent in client.Messages.CreateStreaming(parameters))
{
    if (streamEvent.TryPickContentBlockDelta(out var delta) &&
        delta.Delta.TryPickText(out var text))
    {
        Console.Write(text.Text);
    }
}
```

---

## Tool Use (Manual Loop)

The C# SDK supports raw tool definitions via JSON schema. See the [shared tool use concepts](../shared/tool-use-concepts.md) for the tool definition format and agentic loop pattern.