Dart MCP server does not work in Antigravity

[gryznar]

Steps to reproduce

I am trying to use Dart MCP server in Antigravity. No matter how the path is specified, I still receive
Invalid root file:///D:/Projects/Flutter/my_project/, must be under one of the registered project roots:.
The same configuration from Gemini CLI works as expected: {"roots":[{"root":"file:///D:/Projects/Flutter/my_project/"}]}

[from @antfitch ]
Updated docs for How to set up Antigravity with Dart MCP Server
All, we have updated the steps to use Antigravity with Flutter here: https://docs.flutter.dev/ai/mcp-server#antigravity

[jakemac53]

Yes this is known but thanks for filing the issue.

The workaround for now until Antigravity adds "roots" support is to add the --force-roots-fallback argument to your MCP server invocation. That will switch to a mode where it uses tool calls to manage the roots.

The core issue is that Antigravity claims roots support but never actually sets any roots. This is a very common issue with new MCP clients, they often only support tool calls at first, and the SDK that they use will claim roots support simply because it can respond to the request, even though it always returns an empty list.

[gryznar]

As I understand I should instruct model to use this flag during Dart MCP server invokation?

[jakemac53]

You will have to manually set it in your MCP configuration, in the args section right after mcp-server.

[gryznar]

Ah, okay. Thank you, I'll try it

[twerske]

@antfitch Could we add this to docs while trying to resolve this with the Antigravity team? This is a bug on their MCP set up that we're actively working with them to resolve.

[antfitch]

Yes, let me help with that.

…

On Tue, Nov 25, 2025 at 9:19 AM Emma Twersky ***@***.***> wrote: *twerske* left a comment (dart-lang/ai#322) <#322 (comment)> @antfitch <https://github.com/antfitch> Could we add this to docs while trying to resolve this with the Antigravity team? This is a bug on their MCP set up that we're actively working with them to resolve. — Reply to this email directly, view it on GitHub <#322 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AEMN2EZPHO4OGXQOSPYL4KT36SFRVAVCNFSM6AAAAACND562XKVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTKNZWG4YDKMJYGQ> . You are receiving this because you were mentioned.Message ID: ***@***.***>

[parlough]

Sorry I didn't see your comments @twerske and @antfitch until I finished this.

I prepared flutter/website#12748 which updates the instructions to include the flag alongside some other updates. If you have other changes you'd like to make though, feel free to supersede my PR!

[antfitch]

It appears that @parker Lougheed ***@***.***> has already created a PR for this.

…

On Tue, Nov 25, 2025 at 9:45 AM Amanda Fitch ***@***.***> wrote: Yes, let me help with that. On Tue, Nov 25, 2025 at 9:19 AM Emma Twersky ***@***.***> wrote: > *twerske* left a comment (dart-lang/ai#322) > <#322 (comment)> > > @antfitch <https://github.com/antfitch> Could we add this to docs while > trying to resolve this with the Antigravity team? This is a bug on their > MCP set up that we're actively working with them to resolve. > > — > Reply to this email directly, view it on GitHub > <#322 (comment)>, or > unsubscribe > <https://github.com/notifications/unsubscribe-auth/AEMN2EZPHO4OGXQOSPYL4KT36SFRVAVCNFSM6AAAAACND562XKVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZTKNZWG4YDKMJYGQ> > . > You are receiving this because you were mentioned.Message ID: > ***@***.***> >

[gryznar]

You will have to manually set it in your MCP configuration, in the args section right after mcp-server.

Confirmed. Works. Thanks!

[jakemac53]

I am going to leave this issue open both for discoverability and also tracking the antigravity issue.

[gryznar]

Regarding to Antigravity, I see yet another problem. I am trying to use agent possibility to test Flutter web app, but Gemini constantly claims, it sees nothing (blank screen). App is starting correctly in controlled by antigravity browser via dart-mcp-server / launch_app and setup:

{
  "device": "chrome",
  "root": "d:\\Projects\\Flutter\\my_project"
}

Should I create another issue, or am I doing sth wrong?

[jakemac53]

I am not quite understanding the issue, are those the arguments to a launch_app tool call? What is the exact output you are getting?

[gryznar]

Yes, these are the passed args. Command works as expected (app is launching). What is not working is the fact that model in Antigravity cannot see the browser content. But as I am thinking, this may be strictly related to Antigravity, I suppose. Sorry for the churn, but Antigravity does not have any issue tracker right now?