Resources/read does not return content, specified by [McpMeta] attribute, resources/list does

[Ponomareff]

Describe the bug
Resources/read does not return content, specified by [McpMeta] attribute, resources/list does

To Reproduce
Steps to reproduce the behavior:

1. Attach attribute [McpMeta("ui", JsonValue = """{ "csp": { "resourceDomains": ["https://cdn.jsdelivr.net"] } }""")] to method, marked with [McpServerResource]
2. Using MCP Inspector: resources/list returns _meta attribute value above
3. Using MCP Inspector: resources/read does not

Expected behavior
resources/read returns content of [McpMeta] attribute along with uri, mimeType and text

Additional context
Bug in src\ModelContextProtocol.Core\Server\AIFunctionMcpServerResource.cs method ReadAsync results do not initialize Meta property of returned results

[stephentoub]

Thanks for the issue.

Most of the SDKs don't do this:
#1230 (comment)

Can you elaborate on the need?

[Ponomareff]

Thanks for the issue.

Most of the SDKs don't do this: #1230 (comment)

Can you elaborate on the need?

Short answer: MCP-Apps require this by specification. I confirmed it by fixing on local branch.

https://github.com/modelcontextprotocol/ext-apps/blob/main/specification/2026-01-26/apps.mdx

[stephentoub]

Thanks.

Closing per the discussion in #1230.

You can return results from your resource methods with meta directly populated rather than using attributes.

[ShrayRastogi]

Thanks.

Closing per the discussion in #1230.

You can return results from your resource methods with meta directly populated rather than using attributes.

@stephentoub - However, this solution/workaround does not work for MCP Apps as asked in this question. Perhaps a cleaner sample or approach would help here?

[stephentoub]

Can you elaborate? Why doesn't it work?

[ShrayRastogi]

Can you elaborate? Why doesn't it work?

I have tried with below approaches (with or without McpMeta attribute and also with/without content object) but doesn't work. Using VSCode browse resources feature shows the resource but is unable to open it.

When returning a simple string, you are able to browse the resource but html is not rendered as an MCP App in Chat window because resources/read does not return content specified in McpMeta attribute. The alternative suggested in discussion of #1230 does not work as shown below.

[stephentoub]

In your screenshot you're not returning a ReadResourceResult. Change your method's signature to have that as the return typeand construct one of those instead of an anonymous type.

[ShrayRastogi]

In your screenshot you're not returning a ReadResourceResult. Change your method's signature to have that as the return typeand construct one of those instead of an anonymous type.

@stephentoub - Thanks for the suggestion, however, it still did not work - still no UI rendered. Not sure, if this is a SDK limitation currently, not supporting mcp apps or something else. Hence, I was asking for clear samples/approach.

[stephentoub]

@ShrayRastogi, what does your method signature look like? As I mentioned ("Change your method's signature"), the return type of the method needs to be ReadResourceResult. It can't just be object like in your original example, and it's not just about the concrete type that you return out of the body, but the actual strongly-typed return type in the method signature.