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Build Your First Agent

Time: ~15 minutes
What you'll build: A multi-turn CLI agent with a custom tool, streaming output, and conversation memory.

Prerequisites​

  • .NET 10 SDK
  • AWS credentials with Bedrock access (Claude Haiku or similar)

Step 1: Create the project​

dotnet new console -n MyFirstAgent
cd MyFirstAgent
dotnet add package Jacquard.Core
dotnet add package Jacquard.Models.Bedrock
dotnet add package Jacquard.SourceGenerator

Step 2: Define a tool​

Create WeatherTools.cs:

using Jacquard.Core;

namespace MyFirstAgent;

public partial class WeatherTools
{
    [Tool("Returns the current weather for a city")]
    public string GetWeather(string city) =>
        $"Sunny, 22°C in {city}. Humidity: 45%. Wind: 12 km/h NW.";

    [Tool("Returns a 3-day weather forecast for a city")]
    public string GetForecast(string city) =>
        $"Forecast for {city}: Today sunny 22°C, Tomorrow cloudy 18°C, Day 3 rainy 15°C.";
}

Two things to notice:

  • The class is partial — required for the source generator
  • The [Tool] description is what the model sees when deciding whether to call the tool

Step 3: Create the agent​

Replace Program.cs:

using Jacquard.Core;
using Jacquard.Models.Bedrock;
using MyFirstAgent;

var agent = new Agent(
    model: new BedrockModel(
        region: "us-east-1",
        modelId: "us.anthropic.claude-haiku-4-5-20251001-v1:0"),
    systemPrompt: """
        You are a helpful weather assistant.
        Use the weather tools to answer questions about current conditions and forecasts.
        Be concise and friendly.
        """,
    toolProviders: [new WeatherTools()]);

Console.WriteLine("Weather Assistant — type your question, 'exit' to quit");
Console.WriteLine();

while (true)
{
    Console.ForegroundColor = ConsoleColor.Green;
    Console.Write("You: ");
    Console.ResetColor();

    var input = Console.ReadLine();
    if (string.IsNullOrWhiteSpace(input) || input.Equals("exit", StringComparison.OrdinalIgnoreCase))
        break;

    Console.ForegroundColor = ConsoleColor.Cyan;
    Console.Write("Agent: ");
    Console.ResetColor();

    // Stream the response token by token
    await foreach (var evt in agent.StreamAsync(input))
    {
        if (evt is TextDeltaEvent delta)
            Console.Write(delta.Delta);
    }

    Console.WriteLine();
    Console.WriteLine();
}

Step 4: Run it​

dotnet run

Try these prompts:

  • "What's the weather in London?"
  • "Compare the weather in Tokyo and Sydney"
  • "Should I bring an umbrella to Paris tomorrow?"

The agent will call the appropriate tools and synthesize a response. Because the agent maintains conversation history, you can follow up:

  • "What about the day after?"
  • "Which city has better weather?"

What's happening under the hood​

  1. Your prompt is added to the conversation history
  2. The model receives the history + tool schemas
  3. The model decides to call GetWeather or GetForecast (or both)
  4. The SDK executes the tools and adds results to the history
  5. The model generates a final response using the tool results
  6. The response is streamed back token by token

The partial class WeatherTools becomes an IToolProvider at compile time — the source generator emits the GetTools() implementation. No reflection happens at runtime.

Next steps​