element_builder times out permanently after ~35 minutes of sustained use

[punkhop]

Bug: element_builder times out permanently after ~35 minutes of sustained use

Environment

• MCP Server: Webflow Designer MCP (via Claude Code CLI)
• Browsers tested: Chrome (latest), Safari (latest)
• OS: macOS
• Webflow Plan: Free/Starter
• Date: 2026-03-12

Summary

The element_builder Designer tool works correctly for approximately 35 minutes of sustained use (~50 calls), then begins timing out permanently. No error code is returned — the call simply never resolves (spins indefinitely in the MCP Bridge App UI).

Other Designer tools (style_tool, element_tool, page_tool) continue to work instantly on the same connection. This is not a general MCP connectivity issue — it is specific to element_builder.

Steps to Reproduce

1. Open Webflow Designer with MCP Bridge App connected
2. Use element_builder to create elements on a page — sections, divs, headings, paragraphs, etc.
3. Make approximately 40-50 successful calls over ~35 minutes
4. At some point, element_builder calls stop resolving — they spin forever with no response
5. Verify other tools still work: style_tool (create/update styles), element_tool (get elements, set text), page_tool (switch pages) — all respond instantly

What I tried (none fixed it)

• Refreshing the Designer page (Cmd+R)
• Closing and relaunching the MCP Bridge App
• Switching from Chrome to Safari (completely different browser process)
• Pinning the Designer tab to prevent sleep
• Switching pages within the Designer
• Waiting 30+ minutes before retrying
• Making minimal element_builder calls (single DivBlock, no nesting)

Expected behavior

element_builder should either:

• Continue working after sustained use, OR
• Return a proper error (e.g., HTTP 429 with Retry-After header) instead of hanging indefinitely

Actual behavior

• element_builder hangs forever (no response, no error)
• MCP Bridge App UI shows "Running Element builder" spinner indefinitely
• Red toast errors appear in Designer: "There was an error making your change. Please try again."
• All other Designer MCP tools continue working normally on the same session

Additional context

• The element_builder is labeled "BETA" in the Bridge App UI
• Approximately 50 element_builder calls succeeded before the issue started
• Each call created 1-3 levels of nesting (within the documented 3-level limit)
• Style tool was also used extensively (~30 calls) without any issues
• The issue persists across browser restarts and does not self-resolve within 30+ minutes

Hey @viratatwebflow can you check this out? Appreciate it.

[viratatwebflow]

Hey @punkhop mind contacting via support. Since its related to our Remote MCP. We need few extra details Like site info.

[SirBrenton]

One pattern worth checking here is per-tool capacity exhaustion turning into a permanent unresolved request.

The key signals in the report:

• ~40–50 successful element_builder calls
• ~35 minutes of sustained use
• after that the call never resolves
• other tools (style_tool, element_tool, page_tool) still work on the same session

That combination often points to a tool-specific quota / worker queue being exhausted, where the request enters a wait path but never returns an explicit signal.

A useful reliability invariant for these tool bridges is:

capacity exhaustion must fail fast

If a tool cannot execute due to quota, queue depth, or worker availability, the request should return a structured error (e.g. 429 or explicit capacity error) rather than remaining unresolved indefinitely.

Otherwise transient resource limits degrade into permanent hangs, which is exactly what the reporter is seeing here.

Curious whether element_builder runs through a separate worker / queue path from the other tools.

[viratatwebflow]

reported on support.webflow.com