Where does the bug appear (feature/product)?
Cursor IDE
Describe the Bug
This is an issue with the extension API.
Me and my team are developing Radon IDE, which is an extension for adding extensive support for React Native. We also expose a number of MCP tools.
VSCode exposes vscode.lm.registerTool, which allows MCP tools to be loaded directly, without relying on mcp.json or local Express+MCP servers. Said API is not implemented by Cursor.
In VSCode version 1.105.0, this API was also updated to work with image outputs.
Cursor recently added cursor.mcp.registerServer, but using it is still more convoluted than vscode.lm.registerTool, as to use it locally, we have to manage an Express+MCP server on the user’s machine, which is obliviously not optimal.
Here’s a comparison of how tool registering flow works on VSCode versus Cursor:
// VSCode
1. Define the tool (`vscode.LanguageModelTool<T>`)
2. Declare the tool in `package.json`
3. Register the tool (`vscode.lm.registerTool`)
- To toggle tool availability use `commands.executeCommand("setContext", ...);`
// Cursor
1. Set up an Express server locally
2. Set up an MCP server locally, bind it to the Express server
3. Register the MCP server (`cursor.mcp.registerServer`)
4. Define the tool executor
5. Register the tool in the MCP server
- To toggle tool availability:
1. Unregister/re-register tools in the MCP server.
2. Call `commands.executeCommand("mcp.toolListChanged")` (which is a workaround for https://forum.cursor.com/t/mcp-client-update-tools/77294)
As it can be observed, the VSCode workflow is a fair bit simpler to implement and maintain.
Is there a chance vscode.lm.registerTool will be implemented, or has this already been considered? Thanks in advance.
Steps to Reproduce
- Call
vscode.lm.registerTool - Nothing happens
Expected Behavior
- Call
vscode.lm.registerTool - New MCP tool is present in the tool list
Operating System
MacOS
Current Cursor Version (Menu → About Cursor → Copy)
Version: 2.2.36
VSCode Version: 1.105.1
Commit: 55c9bc11e99cedd1fb93fbb7996abf779c583150
Date: 2025-12-18T06:25:21.733Z
Electron: 37.7.0
Chromium: 138.0.7204.251
Node.js: 22.20.0
V8: 13.8.258.32-electron.0
OS: Darwin arm64 24.5.0
Does this stop you from using Cursor
Sometimes - I can sometimes use Cursor