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fix: improve MCP tool prompt clarity to prevent format confusion #8508

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fix: improve MCP tool prompt clarity to prevent format confusion #8508

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6 changes: 5 additions & 1 deletion src/core/prompts/sections/mcp-servers.ts
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Expand Up @@ -58,7 +58,11 @@ The Model Context Protocol (MCP) enables communication between the system and MC

# Connected MCP Servers

When a server is connected, you can use the server's tools via the \`use_mcp_tool\` tool, and access the server's resources via the \`access_mcp_resource\` tool.
When a server is connected, you MUST use the server's tools via the \`use_mcp_tool\` wrapper, and access the server's resources via the \`access_mcp_resource\` wrapper.

**CRITICAL**: Never call MCP tools directly by their tool name. Always use the \`use_mcp_tool\` wrapper format:
- ❌ WRONG: \`<tool_name>...\</tool_name>\`
- ✅ CORRECT: \`<use_mcp_tool><server_name>...\</server_name><tool_name>...\</tool_name><arguments>...\</arguments>\</use_mcp_tool>\`
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P2: The inline example uses backslashes before closing XML tags (e.g., </server_name>). Within code spans, the backslash will be literal and may lead models to emit a backslash in their tool calls. Remove the backslashes so the example shows proper tags: </server_name>, </tool_name>, , </use_mcp_tool>. This also aligns with the examples in use-mcp-tool.ts.


${connectedServers}`

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40 changes: 33 additions & 7 deletions src/core/prompts/tools/use-mcp-tool.ts
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Expand Up @@ -6,32 +6,58 @@ export function getUseMcpToolDescription(args: ToolArgs): string | undefined {
}
return `## use_mcp_tool
Description: Request to use a tool provided by a connected MCP server. Each MCP server can provide multiple tools with different capabilities. Tools have defined input schemas that specify required and optional parameters.

**IMPORTANT**: You MUST always use the \`use_mcp_tool\` wrapper format shown below. Do NOT call MCP tools directly by their tool name.

Parameters:
- server_name: (required) The name of the MCP server providing the tool
- tool_name: (required) The name of the tool to execute
- arguments: (required) A JSON object containing the tool's input parameters, following the tool's input schema
Usage:

Correct Usage Format:
<use_mcp_tool>
<server_name>server name here</server_name>
<tool_name>tool name here</tool_name>
<arguments>
{
"param1": "value1",
"param2": "value2"
"param1": "value1",
"param2": "value2"
}
</arguments>
</use_mcp_tool>

Example: Requesting to use an MCP tool
❌ INCORRECT - Do NOT use this format:
<get_pull_request>
<owner>username</owner>
<repo>repository</repo>
<pullNumber>123</pullNumber>
</get_pull_request>

✅ CORRECT - Always use this format:
<use_mcp_tool>
<server_name>github</server_name>
<tool_name>get_pull_request</tool_name>
<arguments>
{
"owner": "username",
"repo": "repository",
"pullNumber": 123
}
</arguments>
</use_mcp_tool>

Example: Using a weather MCP tool

<use_mcp_tool>
<server_name>weather-server</server_name>
<tool_name>get_forecast</tool_name>
<arguments>
{
"city": "San Francisco",
"days": 5
"city": "San Francisco",
"days": 5
}
</arguments>
</use_mcp_tool>`
</use_mcp_tool>

Remember: ALWAYS wrap MCP tool calls in the \`use_mcp_tool\` format, never call them directly by their tool name.`
}
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