Step 2: Add Tools

Tools let your agent call custom functions — like fetching weather data, querying a database, or calling an API.

Define a tool as any method with a [Description] attribute:

using System.ComponentModel;

[Description("Get the weather for a given location.")]
static string GetWeather([Description("The location to get the weather for.")] string location)
    => $"The weather in {location} is cloudy with a high of 15°C.";

Create an agent with the tool:

using System;
using Azure.AI.Projects;
using Azure.Identity;
using Microsoft.Agents.AI;
using Microsoft.Extensions.AI;

var endpoint = Environment.GetEnvironmentVariable("AZURE_OPENAI_ENDPOINT")
    ?? throw new InvalidOperationException("Set AZURE_OPENAI_ENDPOINT");
var deploymentName = Environment.GetEnvironmentVariable("AZURE_OPENAI_DEPLOYMENT_NAME") ?? "gpt-4o-mini";

AIAgent agent = new AIProjectClient(new Uri(endpoint), new DefaultAzureCredential())
    .AsAIAgent(
        model: deploymentName,
        instructions: "You are a helpful assistant.",
        tools: [AIFunctionFactory.Create(GetWeather)]);

Warning

DefaultAzureCredential is convenient for development but requires careful consideration in production. In production, consider using a specific credential (e.g., ManagedIdentityCredential) to avoid latency issues, unintended credential probing, and potential security risks from fallback mechanisms.

The agent will automatically call your tool when relevant:

Console.WriteLine(await agent.RunAsync("What is the weather like in Amsterdam?"));

Tip

See here for a full runnable sample application.

Define a tool with the @tool decorator:

# NOTE: approval_mode="never_require" is for sample brevity.
# Use "always_require" in production for user confirmation before tool execution.
@tool(approval_mode="never_require")
def get_weather(
    location: Annotated[str, Field(description="The location to get the weather for.")],
) -> str:
    """Get the weather for a given location."""
    conditions = ["sunny", "cloudy", "rainy", "stormy"]
    return f"The weather in {location} is {conditions[randint(0, 3)]} with a high of {randint(10, 30)}°C."

Create an agent with the tool:

agent = Agent(
    client=client,
    name="WeatherAgent",
    instructions="You are a helpful weather agent. Use the get_weather tool to answer questions.",
    tools=[get_weather],
)

Tip

See the full sample for the complete runnable file.

Next steps

Step 3: Multi-Turn Conversations

Go deeper:

• Tools overview — learn about all available tool types
• Function tools — advanced function tool patterns
• Tool approval — human-in-the-loop for tool calls