Support for Microsoft.Extensions.AI's ForJsonSchema()

[gerwintmg]

Is Microsoft.Extensions.AI's ChatResponseFormatJson.ForJsonSchema() supported with OllamaSharp?

var options = new ChatOptions()
{
	ModelId = "llama3.2-vision",
	ResponseFormat = ChatResponseFormatJson.ForJsonSchema(jsonSchema, schemaName, schemaDescription)
};

[awaescher]

I did not look into that specifically but it seems like what we did with #150.

[gerwintmg]

So there is an implementation, thanks.

I decided to do some debugging and found that the method ToOllamaSharpChatRequest checks for:

Format = (object.Equals(options?.ResponseFormat, ChatResponseFormat.Json) ? "json" : null),

When using ChatResponseFormatJson.ForJsonSchema(jsonSchema, schemaName, schemaDescription) i think this statement is wrong.
As i get a response without json.

after looking at #150 i beleave it should be closer to:

(object.Equals(options?.ResponseFormat, ChatResponseFormat.Json) ? "json" : options?.ResponseFormat)

[Ganesh-403]

@gerwintmg I think you've identified the issue correctly.

ChatResponseFormatJson.ForJsonSchema(...) returns a ChatResponseFormatJson instance, whereas the current implementation appears to only handle the singleton ChatResponseFormat.Json:

Format = object.Equals(options?.ResponseFormat, ChatResponseFormat.Json)
    ? "json"
    : null;

Because of that, schema-based response formats would never be forwarded to Ollama—they'd simply result in Format = null, which explains why the model returns an unconstrained response instead of schema-constrained JSON. Microsoft.Extensions.AI explicitly distinguishes between the generic JSON format (ChatResponseFormat.Json) and schema-based formats created with ForJsonSchema(...). :contentReference[oaicite:0]{index=0}

Looking at Ollama's API, the format field supports either:

• "json" for generic JSON output, or
• a JSON Schema object for structured outputs. :contentReference[oaicite:1]{index=1}

So, assuming ChatRequest.Format is already capable of holding either a string or a schema object, something closer to this would seem more appropriate:

Format = object.Equals(options?.ResponseFormat, ChatResponseFormat.Json)
    ? "json"
    : options?.ResponseFormat;

or, if additional conversion is required, mapping ChatResponseFormatJson into the schema object expected by Ollama.

From what I can tell, the important part is that ChatResponseFormatJson shouldn't be discarded by the equality check. Otherwise, ForJsonSchema(...) can never make it into the outbound request.

If this solves your problem, feel free to mark it as the accepted answer so others can find it easily.