Subagents fail with resource_exhausted when using MCP tools

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1

Where does the bug appear (feature/product)?

Cursor IDE

Describe the Bug

Subagents fail with resource_exhausted when using MCP tools

Summary

Custom subagents work correctly with built-in tools but consistently fail with resource_exhausted error when attempting to use MCP tools (specifically Basecamp MCP).

Environment

  • Cursor Version: 2.4.28
  • OS: macOS
  • Model: Claude Opus 4.5
  • MCP: Basecamp MCP configured and working

Impact

  • Severity: Medium
  • Workaround: Handle MCP-based operations in main agent instead of subagents

This limits the ability to use subagents for context isolation when working with external services via MCP.

Questions

  1. Is MCP tool usage within subagents currently supported, or is this a known limitation?
  2. Is there a way to increase resource allocation for subagents?
  3. Are there plans to address this?

Request ID

3ce789e2-f71d-453d-9f32-4611c313ee5e

Thanks for any help!

Steps to Reproduce

1. Create a simple test subagent (~/.cursor/agents/test-echo.md):

---
name: test-echo
description: Simple test subagent that echoes back what it receives.
---

Echo back whatever you receive and say "Test successful!"

2. Create an MCP-using subagent (~/.cursor/agents/basecamp-context.md):

---
name: basecamp-context
description: Retrieves context from Basecamp cards.
---

You retrieve Basecamp card data. When given a card URL or reference:
1. Parse the project_id and card_id
2. Use get_card(project_id, card_id) to retrieve details
3. Return a summary

3. Test the simple subagent:

Use the test-echo subagent to say hello

Result: :white_check_mark: Works - returns “Test successful!”

4. Test the MCP subagent:

Use the basecamp-context subagent to retrieve card https://3.basecamp.com/xxxxx/buckets/xxxxx/card_tables/cards/xxxxx

Result: :cross_mark: Fails with resource_exhausted

5. Confirm MCP works in main agent:

Call get_card(project_id, card_id) directly from main agent.

Result: :white_check_mark: Works perfectly

Test Results Summary

Test Result
Simple subagent (no tools) :white_check_mark: Works
Subagent + MCP tools :cross_mark: resource_exhausted
MCP tools in main agent :white_check_mark: Works

UI Observations

When the subagent fails, the UI shows:

  • “Explored Thought for 2s”
  • “Thought for 1s”
  • “Work on task attempted”
  • “Task failed”
  • “The subagent is experiencing resource issues.”

No logs appear in ~/.cursor/subagents/ folder (folder doesn’t exist).

Expected Behavior

Custom subagents should be able to use MCP tools, as documented:

Can I use MCP tools in subagents?
Yes. Subagents inherit all tools from the parent, including MCP tools from configured servers.

Source: Subagents | Cursor Docs

Actual Behavior

Subagents that attempt to use MCP tools fail with resource_exhausted error.

Operating System

MacOS

Version Information

  • Cursor Version: 2.4.28

For AI issues: which model did you use?

  • Model: Claude Opus 4.5

For AI issues: add Request ID with privacy disabled

Request ID: 3ce789e2-f71d-453d-9f32-4611c313ee5e

Does this stop you from using Cursor

No - Cursor works, but with this issue

2 Likes
3

Hey, thanks for the detailed bug report.

Looks like this is a real bug. The docs say MCP tools should work in subagents since they inherit tools from the parent, so the resource_exhausted error is unexpected.

Your testing is great. The fact that simple subagents work, and MCP works in the main agent, narrows it down to the subagent plus MCP combination.

I’ll pass this to the team.

For now, your workaround is the right call. Handle MCP operations in the main agent instead of delegating them.

If you hit this with other MCP servers too, not just Basecamp, feel free to add more details here.

1 Like
6

I just want to add that I have this exact same issue even if I do not specifically prompt the main agent to use subagents with MCP tools. Just telling the agent to use a subagent to do a search tasks it still fails with resource_exhausted.

If I disable some of my MCPs and bring the total tool count down the issue does not reproduce. Hope that helps!

1 Like