Non-discarded tab with abnormal state causes `target.asPage()` to hang indefinitely, blocking `browser.pages()`

[so2bin]

Related

#1230, #775

Description

I encountered a variant of the Network.enable timed out issue that has a different root cause than frozen/discarded tabs described in #1230.

In my setup, a specific tab (https://so2bin.github.io/) caused browser.pages() to hang indefinitely, but:

1. The tab was NOT frozen or discarded — it was a normal open tab.
2. 2. Direct CDP Network.enable worked fine on ALL tabs including the problematic one (sub-millisecond response).
3. 3. Puppeteer's target.asPage() was the operation that hung — not Network.enable itself.
4. 4. Refreshing the tab in the browser resolved the issue — suggesting the tab was in some transient abnormal state.
      This means the Chromium-level fix for discarded tabs (https://crrev.com/c/7772775) would NOT address this variant.

Reproduction

1. Connect to Edge browser (Edg/147.0.3912.60) via --browserUrl=http://localhost:9222 from WSL2.
2. 2. Have ~13 page tabs open, including one tab in an abnormal state.
3. 3. Call list_pages or any MCP tool that triggers browser.pages().
4. 4. Observe: the MCP server hangs during initialization and never responds.

Diagnostic Evidence

Step 1: Direct CDP works perfectly on all tabs

Connecting via raw WebSocket to the browser endpoint and manually calling Target.attachToTarget + Network.enable on each of the 13 page targets — all succeed in 0–2ms:

OK  sre / klink-stress / ko-specs-scan · Git  attach=1ms  Network.enable=1ms
OK  KO服务指标面板 - ko - Dashboards - Grafana    attach=1ms  Network.enable=1ms
OK  Tag管理                                   attach=1ms  Network.enable=1ms
...(all 13 pages OK, total 181ms)

Step 2: Puppeteer connect() succeeds, but pages() hangs

const browser = await puppeteer.connect({ browserURL: 'http://localhost:9222' });
// OK in 48ms
const pages = await browser.pages();
// Never returns — hangs indefinitely

Step 3: Isolating the problematic target

Testing target.asPage() individually on each page target:

[0] https://so2bin.github.io/  ... FAIL 6005ms: TIMEOUT  ← ONLY this one hangs
[1] https://fs.dig.kso.net/...  ... OK 7ms
[2] https://sre.kso.net/...     ... OK 3ms
...(all other 13 pages OK in 2-16ms)

Step 4: Refreshing the tab fixes everything

After manually refreshing the so2bin.github.io tab in Edge, browser.pages() and all MCP tools work perfectly.

Key Difference from #1230

	#1230 (frozen/discarded)	This issue
Tab state	Frozen/discarded by memory saver	Normal open tab, not discarded
Network.enable via raw CDP	Times out	Works fine (sub-ms)
Hanging operation	Network.enable in Puppeteer	target.asPage() in Puppeteer
Browser	Chrome on macOS	Edge on Windows (via WSL2)
Fix	Target.activateTarget or Chromium patch	Refresh the tab

Suggested Fix

Since browser.pages() is a blocking all-or-nothing call, a single problematic target blocks the entire MCP server. I suggest:

1. Per-target timeout in pages() enumeration — if asPage() doesn't complete within N seconds for a target, skip it and continue with the remaining targets.
2. 2. Lazy page initialization — don't eagerly call asPage() on all targets during initialization. Only initialize pages on demand when a tool actually needs them.
      This would make chrome-devtools-mcp robust against any type of abnormal tab state, not just the frozen/discarded case.

Environment

• chrome-devtools-mcp version: 0.20.3 and 0.21.0 (both affected)
• • Browser: Microsoft Edge 147.0.3912.60 (Windows)
• • • Puppeteer: 24.40.0 (bundled)
• • • • Node: v22.18.0
• • • • • OS: WSL2 (Ubuntu) connecting to Windows Edge
• • • • • • Connection: --browserUrl=http://localhost:9222

[OrKoN]

We do not support Edge. Does it reproduce with Google Chrome?

[OrKoN]

asPage is only called for extension targets, the feature that is disabled by default.

[so2bin]

Thanks for the quick response @OrKoN.

I don't have Chrome installed in my current setup, so I'm unable to confirm whether this reproduces on Chrome. Since Edge is not supported, feel free to close this issue. If I get a chance to test with Chrome later, I'll report back.