Capture console output from content script isolated worlds

[BenRacicot]

Description of the bug

Console messages from Chrome extension content scripts (which run in isolated execution contexts) are not captured by list_console_messages. Only main-world logs (from page scripts or evaluate_script) are visible.

Environment

• chrome-devtools-mcp v0.17.3
• Chrome stable channel
• Using via Claude Code

Observed behavior

Content scripts that write to the DOM work fine — attributes set by content scripts are visible via snapshots. However, console.log() calls from those same content scripts are never surfaced by list_console_messages.

Source	Captured?
Page scripts (main world)	✅ Yes
evaluate_script calls	✅ Yes
Content script console.log (isolated world)	❌ No
Content script DOM writes	✅ Yes (via snapshots)

Root cause

This appears to be a CDP configuration gap rather than a bug. Chrome content scripts run in isolated execution contexts, and Runtime.enable only subscribes to main-world console output by default. To capture logs from content scripts, the server would need to:

1. Listen for Runtime.executionContextCreated events
2. Call Runtime.enable for each new isolated execution context (where context.auxData.isDefault === false)

The CDP plumbing for this exists — it's just not currently wired up in the MCP server.

Use case

Developing and debugging Chrome extensions with an AI coding agent. The agent needs to verify that content scripts are loading and executing correctly, which currently requires workarounds like bridging content script output to the main world via DOM attributes and MutationObservers.

Current workaround

A MutationObserver bridge in the main world that watches for DOM attribute changes made by the content script, then re-emits them as main-world console.log calls — making them visible to list_console_messages. This works but adds complexity.

Suggested implementation

In the CDP session setup, subscribe to execution context creation and enable runtime reporting for isolated worlds:

client.on('Runtime.executionContextCreated', ({ context }) => {
  if (!context.auxData?.isDefault) {
    // This is an isolated world (content script)
    client.send('Runtime.enable', {}, context.id);
  }
});

This would make list_console_messages capture logs from all execution contexts, not just the main world.

Reproduction

No response

Expectation

No response

MCP configuration

No response

Chrome DevTools MCP version

0.17.3

Chrome version

146

Coding agent version

No response

Model version

No response

Chat log

No response

Node version

24

Operating system

macOS

Extra checklist

• I want to provide a PR to fix this bug

[OrKoN]

I think this makes sense as a feature request and it would be largely in scope for #96 keeping as a separate issue to make sure it is not forgotten.

[nroscino]

This has been resolved within puppeteer. A test proving this works was introduced in: #1920