Return content array so tools like claude code can provide nice formatting of output

[machow]

Describe the bug

Currently, tool calls for services like gmail often return a response of form:

{ "result": "Retrieved X messages ... <long string>" }

However, I think things like claude code often expect, and can nicely format messages when they're this format:

{
  "result":  {
    "content": [ {"type": "text", "text": "Retrieved X messages ..."}, ...]
  }
}

For example, here is the mcp tool execution result example in the mcp docs.

I noticed that tools like https://github.com/GongRzhe/Gmail-MCP-Server use this content array format, and the outputs are nicely displayed. I'm loving using google_workspace_mcp but it's a bit tougher to glance at the results in claude code. WDYT of returning something like a content array?

In any event, thanks so much for this great tool!

To Reproduce

Run a gmail tool call in claude code (e.g. search_gmail_messages).

Expected behavior

The entries are cleanly separated with a blank line between them. Currently, I see something like this...

In Gmail-MCP-Server it looks like this

[machow]

I did some tinkering in the repo, and am a bit surprised since...

• Based on this FastMCP doc, it should automatically upgrade the str result in search_gmail_messages to TextContent
• When I manually wrap the result of search_gmail_messages in TextContent I get the desired output!

Not sure why it isn't automatically upgraded to TextContent by FastMCP?!

edit: possibly related to jlowin/fastmcp#2068

edit2: the code in FastMCP to convert results is pretty simple and seems to handle strings. It's run as middleware though, so maybe something funky happens when this library tweaks the middleware for oauth or something? I'm stumped! conversion code and tool middleware injection code

last edit: okay, it looks like structured content does not get automatically converted, and that is was claude code is using? (due to the "result" field being added in the claude code output). See https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/tools/tool.py#L363-L365