Cursor-agent CLI: MCP tool calls silently stopped working in 2026.04.17

Support Bug Reports
,
1

Where does the bug appear (feature/product)?

Cursor CLI

Describe the Bug

MCP tool calls (mcpToolCall events) work in cursor-agent 2026.04.14-ee4b43a and silently fail in 2026.04.17-479fd04.

The agent sees MCP tool descriptors (verified via cursor-agent mcp list showing the server as “ready”), but when it tries to use a tool, zero mcpToolCall events are emitted. Instead the agent falls back to read-only listMcpResources/readMcpResource probes, then gives up or tries shell workarounds.

This is a regression — the same workspace, config, and prompts work on 2026.04.14 and fail on 2026.04.17.

Steps to Reproduce

  1. Create a workspace with .cursor/mcp.json defining a tools-only MCP server (one that exposes tools but no resources)
  2. Verify the server is ready: cursor-agent mcp list shows it as “ready”
  3. Run with the working version:
~/.local/share/cursor-agent/versions/2026.04.14-ee4b43a/cursor-agent \
  -p "Call the hoover MCP server's recall tool with query 'test'" \
  --workspace /path/to/workspace \
  --model claude-4-sonnet \
  --output-format stream-json \
  --approve-mcps \
  --trust \
  --force
  1. Observe mcpToolCall events in the stream-json output
  2. Run the same command with the broken version:
~/.local/share/cursor-agent/versions/2026.04.17-479fd04/cursor-agent \
  -p "Call the hoover MCP server's recall tool with query 'test'" \
  --workspace /path/to/workspace \
  --model claude-4-sonnet \
  --output-format stream-json \
  --approve-mcps \
  --trust \
  --force
  1. Observe zero mcpToolCall events — only listMcpResourcesToolCall and readMcpResourceToolCall

Expected Behavior

Agent emits mcpToolCall event when invoking an MCP tool:

{
  "type": "mcpToolCall",
  "providerIdentifier": "hoover",
  "toolName": "recall",
  "arguments": { "query": "test" }
}

This is what happens on 2026.04.14-ee4b43a.

ACTUAL BEHAVIOR

Agent emits only:

  • listMcpResourcesToolCall (finds no resources — server is tools-only)
  • readMcpResourceToolCall (fails — no resources to read)
  • Falls back to shell commands or gives up

Zero mcpToolCall events appear in the stream-json output.

Operating System

MacOS

Version Information

Working:
CLI Version 2026.04.14-ee4b43a

Broken:
CLI Version 2026.04.17-479fd04

For AI issues: which model did you use?

claude-4-sonnet (also reproduced with composer-2-fast and gpt-5.3-codex-fast — same behavior)

Additional Information

Impact:

  • Any MCP server that exposes tools but no resources is effectively unusable from cursor-agent CLI on 2026.04.17
  • The Cursor IDE is unaffected — CallMcpTool works there
  • Test harnesses that drive cursor-agent for automated MCP validation break silently

Workaround:
Pin to 2026.04.14-ee4b43a:

export CURSOR_AGENT_BIN="$HOME/.local/share/cursor-agent/versions/2026.04.14-ee4b43a/cursor-agent"

Evidence:

  • Ran identical test scenarios against both versions with same workspace, .cursor/mcp.json, model, and MCP approval state
  • Working version: 3 mcpToolCall events (full pipeline fired)
  • Broken version: 0 mcpToolCall events (agent used listMcpResources, then shell)

Related:

  • A separate test harness (project-nav) confirmed MCP tool calls working on 2026-04-14 (25/28 runs had mcpToolCall events)
  • This regression was initially misdiagnosed as “cursor-agent CLI doesn’t support MCP tool calls” — it does, but only on older versions

Does this stop you from using Cursor

Sometimes - I can sometimes use Cursor