[mcp] Cannot use multiple MCP servers (MCPToolSets) with Agent

[tstadel]

Describe the bug
Maybe I'm missing something but from the definition of Agent's tools init param, one can pass only a list of Tool or one ToolSet. For MCP servers we have MCPToolSet. So we can only use one MCPServer. This is a heavy limitation if you want to use, e.g. github MCP server and gmail MCP server together.

Agent's tool definition:
https://github.com/deepset-ai/haystack/blob/2a27e0d13193fd3910600ef2cbda21cabc2da659/haystack/components/agents/agent.py#L100

MCPToolSet:

haystack-core-integrations/integrations/mcp/src/haystack_integrations/tools/mcp/mcp_toolset.py

Line 30 in c633ac1

class MCPToolset(Toolset):

To Reproduce

Describe your environment (please complete the following information):

• OS: [e.g. iOS]
• Haystack version: 2.18.0
• Integration version: 0.7.0

[vblagoje]

Hmm, that should work, see https://github.com/vblagoje/itinerary-agent/blob/main/itinerary_agent.py#L100 how I used here bunch of different MCPToolset(s)

[sjrl]

@tstadel, @vblagoje and I discussed offline that even though mcp tool sets can be combined that the serialization and deserialization of the new combined toolset may break

[tstadel]

@sjrl ok thx good to know. Will there be a fix soon?

[vblagoje]

I'll see to have this one for next weeks sprint as we are also adding the Tool warmup so all Tools that need some resource init (like MCP) work better in no-code env.

How would you want the solution for this issue to look like, ideally, @tstadel ?

[tstadel]

I'll see to have this one for next weeks sprint as we are also adding the Tool warmup so all Tools that need some resource init (like MCP) work better in no-code env.

How would you want the solution for this issue to look like, ideally, @tstadel ?

Sounds good. Ideally, we can pass in any amount of mcp servers and tools to Agent. So the signature of the Agent's tools init param would be something like tools: list[Tool | ToolSet] | None

[vblagoje]

Supported in https://pypi.org/project/mcp-haystack/0.9.0/ and https://pypi.org/project/haystack-ai/2.19.0/ Closing