microsoft/semantic-kernel · error · ArgumentException

Unsupported agent type: {agentType}

Error message

Unsupported agent type: {agentType}

What it means

Error "Unsupported agent type: {agentType}" thrown in microsoft/semantic-kernel.

Source

Thrown at dotnet/samples/Demos/A2AClientServer/A2AServer/HostAgentFactory.cs:27

using Microsoft.SemanticKernel.Agents.AzureAI;

namespace A2AServer;

internal static class HostAgentFactory
{
    internal static async Task<A2AHostAgent> CreateFoundryHostAgentAsync(string agentType, string modelId, string endpoint, string assistantId, IEnumerable<KernelPlugin>? plugins = null)
    {
        var agentsClient = new PersistentAgentsClient(endpoint, new AzureCliCredential());
        PersistentAgent definition = await agentsClient.Administration.GetAgentAsync(assistantId);

        var agent = new AzureAIAgent(definition, agentsClient, plugins);

        AgentCard agentCard = agentType.ToUpperInvariant() switch
        {
            "INVOICE" => GetInvoiceAgentCard(),
            "POLICY" => GetPolicyAgentCard(),
            "LOGISTICS" => GetLogisticsAgentCard(),
            _ => throw new ArgumentException($"Unsupported agent type: {agentType}"),
        };

        return new A2AHostAgent(agent, agentCard);
    }

    internal static async Task<A2AHostAgent> CreateChatCompletionHostAgentAsync(string agentType, string modelId, string apiKey, string name, string instructions, IEnumerable<KernelPlugin>? plugins = null)
    {
        var builder = Kernel.CreateBuilder();
        builder.AddOpenAIChatCompletion(modelId, apiKey);
        if (plugins is not null)
        {
            foreach (var plugin in plugins)
            {
                builder.Plugins.Add(plugin);
            }
        }
        var kernel = builder.Build();

View on GitHub (pinned to c028a0c7dc)

Solutions

1. Use one of the supported agent type strings accepted by HostAgentFactory (check the factory's switch/case for valid values).
2. If a new agent type is needed, extend HostAgentFactory with a branch for that type.

When it happens

Trigger: Thrown at dotnet/samples/Demos/A2AClientServer/A2AServer/HostAgentFactory.cs:27 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of microsoft/semantic-kernel@c028a0c7dc (2026-08-13). Data as JSON: /api/errors/4d1c013ef59adf02. Report an issue: GitHub.