microsoft/semantic-kernel · error · NotSupportedException

Unsupported chat message content type '{item.GetType()}'.

Error message

Unsupported chat message content type '{item.GetType()}'.

What it means

Thrown inside the multi-part User message builder. It maps each KernelContent item to an OpenAI content part for TextContent, ImageContent, AudioContent, and BinaryContent. Any other KernelContent-derived type (e.g. FunctionCallContent, a custom content subclass) has no wire representation in a user message, so it is rejected.

Source

Thrown at dotnet/src/Connectors/Connectors.OpenAI/Core/ClientCore.ChatCompletion.cs:805

            throw new NotSupportedException("No function result provided in the tool message.");
        }

        if (message.Role == AuthorRole.User)
        {
            if (message.Items is { Count: 1 } && message.Items.FirstOrDefault() is TextContent textContent)
            {
                return [new UserChatMessage(textContent.Text) { ParticipantName = message.AuthorName }];
            }

            return
            [
                new UserChatMessage(message.Items.Select(static (KernelContent item) => item switch
                    {
                        TextContent textContent => ChatMessageContentPart.CreateTextPart(textContent.Text),
                        ImageContent imageContent => GetImageContentItem(imageContent),
                        AudioContent audioContent => GetAudioContentItem(audioContent),
                        BinaryContent binaryContent => GetBinaryContentItem(binaryContent),
                        _ => throw new NotSupportedException($"Unsupported chat message content type '{item.GetType()}'.")
                    }))
                { ParticipantName = message.AuthorName }
            ];
        }

        if (message.Role == AuthorRole.Assistant)
        {
            var toolCalls = new List<ChatToolCall>();

            // Handling function calls supplied via either:
            // ChatCompletionsToolCall.ToolCalls collection items or
            // ChatMessageContent.Metadata collection item with 'ChatResponseMessage.FunctionToolCalls' key.
            IEnumerable<ChatToolCall>? tools = (message as OpenAIChatMessageContent)?.ToolCalls;
            if (tools is null && message.Metadata?.TryGetValue(OpenAIChatMessageContent.FunctionToolCallsProperty, out object? toolCallsObject) is true)
            {
                tools = toolCallsObject as IEnumerable<ChatToolCall>;
                if (tools is null && toolCallsObject is JsonElement { ValueKind: JsonValueKind.Array } array)
                {

View on GitHub (pinned to c028a0c7dc)

Solutions

1. Keep user-role Items limited to TextContent, ImageContent, AudioContent, and BinaryContent.
2. Move function-call content to an Assistant-role message instead.
3. If you have a custom content type, flatten it to TextContent before adding to a user message.

Example fix

// before
userMsg.Items.Add(new FunctionCallContent("foo", "bar"));
// after
userMsg.Items.Add(new TextContent("called foo"));

static bool IsSupportedUserContent(KernelContent c) => c is TextContent or ImageContent or AudioContent or BinaryContent;

static bool UserItemsAllSupported(ChatMessageContent m) => m.Role == AuthorRole.User && m.Items.All(IsSupportedUserContent);

try { await client.GetChatCompletionAsync(history); }
catch (NotSupportedException ex) when (ex.Message.Contains("content type")) { /* strip unsupported items */ }

When it happens

Trigger: A user-role ChatMessageContent whose Items collection contains a content type other than the four supported ones — for example a FunctionCallContent or a custom content class added to the items list.

Common situations: Reusing a message's Items collection across roles; programmatically merging function-call content into a user message; third-party content extensions not yet mapped by the connector.

Related errors

• Failed to get a response from the chat completion service.
• The provided reasoning effort '{textEffortLevel}' is not sup
• The provided reasoning effort '{effortLevelObject.GetType()}
• The provided web search options '{executionSettings.WebSearc
• Role {message.Role} is not supported.

AI-assisted analysis of microsoft/semantic-kernel@c028a0c7dc (2026-08-13). Data as JSON: /api/errors/3f4432c8f2dda8c1. Report an issue: GitHub.