v0.20.1 breaks Electron apps: Target.getDevToolsTarget wasn't found

[churnish]

Description

v0.20.1 breaks all tool calls when connecting to Electron apps (e.g. Obsidian) via --browser-url. Every tool call fails with:

Protocol error (Target.getDevToolsTarget): 'Target.getDevToolsTarget' wasn't found

v0.20.0 works fine with the same setup.

Root cause

PR #1150 replaced the loop-based DevTools window detection with page.hasDevTools(), which calls Target.getDevToolsTarget — a CDP method that Electron's CDP implementation doesn't expose.

The call happens in McpContext.detectOpenDevToolsWindows() (line 475), which runs on every list_pages and page selection, making the entire MCP unusable.

Environment

• chrome-devtools-mcp: 0.20.1
• Electron: 39.7.0 (Chrome 142.0.7444.265)
• App: Obsidian 1.12.4
• Connection: --browser-url=http://127.0.0.1:9222

Workaround

Wrap the hasDevTools() call in a try-catch in build/src/McpContext.js:

try {
    if (await page.hasDevTools()) {
        mcpPage.devToolsPage = await page.openDevTools();
    } else {
        mcpPage.devToolsPage = undefined;
    }
} catch {
    // Target.getDevToolsTarget not supported (e.g. Electron)
    mcpPage.devToolsPage = undefined;
}

Expected behavior

list_pages and other tools should work with Electron apps that don't support Target.getDevToolsTarget, gracefully skipping DevTools window detection.

🤖 Generated with Claude Code

[Igloczek]

Same problem on my end, reverting to 0.20.0 fixes the issue.

[vmklvm]

yea, something wrong

[martinambrus]

I can confirm latest update broke even Claude Code with the same error - browser opens but Claude can't continue using the MCP because of this

[wolfib]

Thank you for the bug report. #1150 has been reverted and a new release 0.20.2 has been created.

[Lightning00Blade]

Hello,

You are seeing this as the underlying version of Chrome (Chromium) is too old and does not match the current stable version of Chrome - 146.0.7680.80.
The change was introduced in 144.0.7559.59 which has been stable for quite some time.
Please consider updating to a newer version to ensure the MCP is working as intended.

[churnish]

Apps like Obsidian bump Electron version only periodically; I'm on the latest supported build. That's why backwards compatibility with slightly older Chromium versions is desirable. (Though I now have no issues on 0.20.2.)

[Igloczek]

@Lightning00Blade please consider not enforcing usage of a recent, not widely available API, without any fallback, published in a hotfix release, without clearly describing it as a breaking change in the changelog

[Lightning00Blade]

Hey @Igloczek ,
As you can see from my previous, the API is widely available for some time on Chrome stable, so the change is non breaking from Chrome perspective, which is the supported product.
I think a middle ground is as you describe a fallback, like the one that was suggested from the reporter, that could be release as a new version, given it's low cost of maintenance.

[Igloczek]

@Lightning00Blade if it was actually so widely available and not breaking, this issue won't exist