MCP configuration Environment Variable expansion does not support ${workspaceFolder}

[axmo]

App Version

Roo Code 3.18.3
VSCode 1.100.2
macOS 15.4.1

API Provider

Not Applicable / Other

Model Used

N/A

🔁 Steps to Reproduce

1. install docker desktop
2. docker pull mcp/filesystem
3. create the following MCP configuration:

"mcpServers": {
  "filesystem": {
    "command": "docker",
    "args": [
      "run",
      "-i",
      "--rm",
      "--mount", "${workspaceFolder}",
      "mcp/filesystem",
      "/projects"
    ]
  }
}

Filesystem MCP is used here as a simple example, but any dockerized MCP server that needs access to the files in the workspace will have this problem.

💥 Outcome Summary

Expected Result:

• dockerized filesystem MCP server run with the current workspace folder mounted to /projects within the container

Actual result: Filesystem MCP server fails to run.

📄 Relevant Logs or Errors (Optional)

Server "filesystem" info: invalid argument "type=bind,src=${workspaceFolder}" for "--mount" flag: target is required ...

note that ${workspaceFolder} has been included verbatim in the argument, instead of the actual path to the workspace.

[hannesrudolph]

I'm temporarily closing this issue as can't reproduce, but to clarify: your description likely does capture the issue, just not yet clearly enough for our updated reporting standards.

I know this is a shift from previous practices, but we're now emphasizing structured reproduction steps to make sure we can quickly:

• Confirm the issue exactly as you're seeing it.
• Clearly determine when a fix resolves the issue.
• Avoid ambiguity when testing internally.

Could you please update your report with:

• Explicitly numbered steps someone else can reliably follow.
• Specific expected vs actual behavior, or exact error messages.
• Complete environment details (OS, IDE, exact software versions).

I appreciate your patience as we adapt to this new structure. Once you've refined the steps, I'll immediately reopen this issue and push it forward internally.

[NamesMT]

Hi @hannesrudolph, please help re-open the issue, this feature is a requirement for MCPs like @modelcontextprotocol/filesystem, so that the MCP can (automatically) infer the current workspace folder.

Without this we will be fairly behind from other clients in term of MCPs support.

Btw, it is not exclusive for only dockerized MCPs like @axmo reported, though dockerized MCPs will definitely be the main usecase for this variable support.

It seems like @axmo have also edited the post a bit according to your requirement.

[daniel-lxs]

Hi @axmo, could you please check if PR #3970, which enables environment variable expansion in MCP server configurations including args, resolves the issue you described with ${workspaceFolder}? Thank you!