Microsoft.Extensions.AI Integration

Cross-SDK comparison

See the centralized MEAI documentation for feature matrices and comparisons across all tryAGI SDKs.

The RetellAI SDK provides AIFunction tool wrappers compatible with Microsoft.Extensions.AI. These tools can be used with any IChatClient to give AI models the ability to manage Retell AI voice agents, phone calls, and phone numbers.

Installation

dotnet add package RetellAI

List Agents Tool

Use AsListAgentsTool() to create an AIFunction that lists all Retell AI voice agents.

using Microsoft.Extensions.AI;
using RetellAI;

var retellClient = new RetellAiClient(
    apiKey: Environment.GetEnvironmentVariable("RETELLAI_API_KEY")!);

AIFunction listAgentsTool = retellClient.AsListAgentsTool(limit: 20);

// Use with any IChatClient (OpenAI, Anthropic, Ollama, etc.)
IChatClient chatClient = /* your chat client */;

var options = new ChatOptions
{
    Tools = [listAgentsTool],
};

var response = await chatClient.GetResponseAsync(
    "What voice agents do I have configured?",
    options);

Console.WriteLine(response.Text);

Get Agent Tool

Use AsGetAgentTool() to create an AIFunction that retrieves details of a specific agent.

using Microsoft.Extensions.AI;
using RetellAI;

var retellClient = new RetellAiClient(
    apiKey: Environment.GetEnvironmentVariable("RETELLAI_API_KEY")!);

AIFunction getAgentTool = retellClient.AsGetAgentTool();

IChatClient chatClient = /* your chat client */;

var options = new ChatOptions
{
    Tools = [getAgentTool],
};

var response = await chatClient.GetResponseAsync(
    "Get the details of agent oBeDLoLOeuAbiuaMFXRtDOLriTJ5tSxD",
    options);

Console.WriteLine(response.Text);

Create Phone Call Tool

Use AsCreatePhoneCallTool() to create an AIFunction that initiates outbound phone calls.

using Microsoft.Extensions.AI;
using RetellAI;

var retellClient = new RetellAiClient(
    apiKey: Environment.GetEnvironmentVariable("RETELLAI_API_KEY")!);

AIFunction createCallTool = retellClient.AsCreatePhoneCallTool();

IChatClient chatClient = /* your chat client */;

var options = new ChatOptions
{
    Tools = [createCallTool],
};

var messages = new List<ChatMessage>
{
    new(ChatRole.User,
        "Call +12137774445 from +14157774444 using my support agent."),
};

while (true)
{
    var response = await chatClient.GetResponseAsync(messages, options);
    messages.AddRange(response.ToChatMessages());

    if (response.FinishReason == ChatFinishReason.ToolCalls)
    {
        var results = await response.CallToolsAsync(options);
        messages.AddRange(results);
        continue;
    }

    Console.WriteLine(response.Text);
    break;
}

List Calls Tool

Use AsListCallsTool() to create an AIFunction that lists recent voice calls.

using Microsoft.Extensions.AI;
using RetellAI;

var retellClient = new RetellAiClient(
    apiKey: Environment.GetEnvironmentVariable("RETELLAI_API_KEY")!);

AIFunction listCallsTool = retellClient.AsListCallsTool(limit: 20);

IChatClient chatClient = /* your chat client */;

var options = new ChatOptions
{
    Tools = [listCallsTool],
};

var response = await chatClient.GetResponseAsync(
    "Show me the most recent voice calls.",
    options);

Console.WriteLine(response.Text);

Get Call Details Tool

Use AsGetCallTool() to create an AIFunction that retrieves details of a specific call, including its transcript.

using Microsoft.Extensions.AI;
using RetellAI;

var retellClient = new RetellAiClient(
    apiKey: Environment.GetEnvironmentVariable("RETELLAI_API_KEY")!);

AIFunction getCallTool = retellClient.AsGetCallTool();

IChatClient chatClient = /* your chat client */;

var options = new ChatOptions
{
    Tools = [getCallTool],
};

var response = await chatClient.GetResponseAsync(
    "Get the transcript and details for call Jabr9TXYYJHfvl6Syypi88rdAHYHmcq6",
    options);

Console.WriteLine(response.Text);

List Phone Numbers Tool

Use AsListPhoneNumbersTool() to create an AIFunction that lists all configured phone numbers.

using Microsoft.Extensions.AI;
using RetellAI;

var retellClient = new RetellAiClient(
    apiKey: Environment.GetEnvironmentVariable("RETELLAI_API_KEY")!);

AIFunction listPhoneNumbersTool = retellClient.AsListPhoneNumbersTool();

IChatClient chatClient = /* your chat client */;

var options = new ChatOptions
{
    Tools = [listPhoneNumbersTool],
};

var response = await chatClient.GetResponseAsync(
    "What phone numbers do I have available?",
    options);

Console.WriteLine(response.Text);

Combining All Tools

You can provide all six tools simultaneously, letting the model decide which to use.

using Microsoft.Extensions.AI;
using RetellAI;

var retellClient = new RetellAiClient(
    apiKey: Environment.GetEnvironmentVariable("RETELLAI_API_KEY")!);

var options = new ChatOptions
{
    Tools =
    [
        retellClient.AsListAgentsTool(),
        retellClient.AsGetAgentTool(),
        retellClient.AsCreatePhoneCallTool(),
        retellClient.AsListCallsTool(),
        retellClient.AsGetCallTool(),
        retellClient.AsListPhoneNumbersTool(),
    ],
};

IChatClient chatClient = /* your chat client */;

var messages = new List<ChatMessage>
{
    new(ChatRole.User,
        "Check what phone numbers I have, then list my agents. " +
        "If I have both, make a call from the first number to +12025551234."),
};

while (true)
{
    var response = await chatClient.GetResponseAsync(messages, options);
    messages.AddRange(response.ToChatMessages());

    if (response.FinishReason == ChatFinishReason.ToolCalls)
    {
        var results = await response.CallToolsAsync(options);
        messages.AddRange(results);
        continue;
    }

    Console.WriteLine(response.Text);
    break;
}

Tool Details

Method	Tool Name	Description
AsListAgentsTool()	ListRetellAgents	Lists all voice agents with IDs, names, and status
AsGetAgentTool()	GetRetellAgent	Gets details of a specific agent by ID
AsCreatePhoneCallTool()	CreateRetellPhoneCall	Creates an outbound phone call
AsListCallsTool()	ListRetellCalls	Lists recent voice calls with status and duration
AsGetCallTool()	GetRetellCall	Gets call details including transcript and recording
AsListPhoneNumbersTool()	ListRetellPhoneNumbers	Lists all configured phone numbers

AsListAgentsTool Parameters

Parameter	Type	Default	Description
limit	int	50	Maximum number of agents to return

AsListCallsTool Parameters

Parameter	Type	Default	Description
limit	int	50	Maximum number of calls to return