Add default MCP servers to extension

[nordanz]

Hello There,

Is it possible to register MCP servers within my extension. my extension contains an AI agent and should use some default MCP servers. What would be the injectable service or is there any?

[msujew]

cc @sdirix

[sdirix]

Hi!

In case you are using the Theia IDE, then you can add MCP servers via preferences. Afterwards you can start them manually, or configure autostart for them. The tools registered by the MCP server are then available to all agents. However to make use of them, you need to refer to them in the agent's prompts. For more information, see the MCP Integration chapter of the user documentation.

If you are implementing an own Theia extension, then you can do the same, but you also have additional options available:

• You can register MCP servers programmatically via addOrUpdateServer of the MCPServerManager in the Theia backend or frontend
• Besides mentioning the registered tool calls of the MCP server in agent prompts, you could also add the tools manually:
  • In your chat agent you can override the sendLlmRequest method and append your tools to the handed over toolRequests, or
  • You can in general overwrite the sendRequest method of the LanguageModelService. All requests to LLMs go through this method, so you can add your custom tools here in a single place without touching any of the builtin agents.

Is that what you are looking for? Let me know in case you need more information.

[nordanz]

Thanks @sdirix for the prompt reply. Yes, I'm building a custom Theia with previous installed stuff like my MCP server, so I believe I need the MCPServerManager that not only my custom agent, but other agents as well have access to it. so, the right way would be to inject this class to my agent class and then add a server to it? am I right?

[sdirix]

I would inject the MCPServerManager in a FrontendApplicationContribution or BackendApplicationContribution and then manage your server there. This makes sure that your MCP server is added (and potentially started) on startup.

Note that you can also contribute MCP servers via VS Code extensions. So if that is also of interest for you, then you could also go this route.

[fipro78]

@sdirix
I am trying to compare the available approaches you mentioned. For the VS Code extension I have provided a PR to support the remote mcp servers. That works.

I created a FrontendApplicationContribution and registered the mcp servers programmatically there. That also works.

I tried to create a BackendApplicationContribution to register the mcp servers programmatically. But that does not work. I am not able to get the MCPServerManager injected there.

Error: No matching bindings found for serviceIdentifier: Symbol(MCPServerManager)

Is something missing in https://github.com/eclipse-theia/theia/blob/master/packages/ai-mcp/src/node/mcp-backend-module.ts to make the MCPServerManager also available for injection in the backend side, or is there another way to get it there? in the FrontendApplicationContribution it can be simply injected.

[sdirix]

Hi @fipro78,

Most Theia AI backend services are bound in a ConnectionContainerModule instead of a regular container. The key difference is that a ConnectionContainerModule is created per frontend connection, so its lifetime is tied to the specific frontend. In a regular container, services exist independently of any frontend.

This setup allows each frontend (each open tab or window) to manage its AI functionality separately, including its own MCP server.

To access the existing MCPServerManager, you need to do it within a ConnectionContainerModule. You can see an example of how the ConnectionContainerModule is used here in the MCP package.