MCP Tool YAML Config

MCP Tool YAML Configuration Implementation

Overview

Implement YAML configuration support for enabling/disabling individual MCP tools while maintaining proper precedence: CLI/env > YAML > default (all enabled).

Current State

The codebase already has:

• Tool control via CLI/env: --tools / MCP_TOOLS specifies list of enabled tools
• MCP config structure: MCPAgentConfig extends AgentConfig with mcp.tools for per-tool overrides (currently only description and argument_descriptions)
• Tool registration: NextGenUIMCPServer._setup_mcp_tools() registers tools with enabled= flag based on self.enabled_tools list

MCP_ALL_TOOLS = [
    "generate_ui_component",
    "generate_ui_multiple_components",
]

        if enabled_tools:
            for t in enabled_tools:
                if t not in MCP_ALL_TOOLS:
                    raise ValueError(
                        f"tool '{t}' is no valid. Available tools are: {MCP_ALL_TOOLS}"
                    )
            self.enabled_tools = enabled_tools
        else:
            self.enabled_tools = MCP_ALL_TOOLS

Implementation Steps

1. Extend Configuration Schema

File: [libs/next_gen_ui_mcp/agent_config.py](libs/next_gen_ui_mcp/agent_config.py)

Add enabled field to MCPAgentToolConfig:

class MCPAgentToolConfig(BaseModel):
    """Information to override default values in the MCP Agent tool."""

    enabled: Optional[bool] = Field(
        description="Whether the tool is enabled. Defaults to True.",
        default=None,
    )
    
    description: Optional[str] = Field(...)
    argument_descriptions: Optional[dict[str, str]] = Field(...)

2. Implement Precedence Logic

File: [libs/next_gen_ui_mcp/agent.py](libs/next_gen_ui_mcp/agent.py)

Update NextGenUIMCPServer.__init__() to merge configurations with precedence:

Current logic (lines 198-206):

• If enabled_tools parameter is provided → use it
• Otherwise → use MCP_ALL_TOOLS

New logic should:

1. Start with default: all tools enabled
2. Apply YAML config: disable tools where config.mcp.tools.<tool>.enabled = False
3. Apply CLI/env override: if enabled_tools parameter provided, use it (ignore YAML)
4. Validate all tool names

Example implementation:

# In __init__ around line 198
if enabled_tools:
    # CLI/env has highest precedence
    for t in enabled_tools:
        if t not in MCP_ALL_TOOLS:
            raise ValueError(f"tool '{t}' is not valid. Available tools are: {MCP_ALL_TOOLS}")
    self.enabled_tools = enabled_tools
else:
    # Start with all tools enabled
    self.enabled_tools = list(MCP_ALL_TOOLS)
    
    # Apply YAML config if present
    if self.config.mcp and self.config.mcp.tools:
        tools_config = self.config.mcp.tools
        for tool_name in MCP_ALL_TOOLS:
            tool_config = getattr(tools_config, tool_name, None)
            if tool_config and tool_config.enabled is False:
                if tool_name in self.enabled_tools:
                    self.enabled_tools.remove(tool_name)

3. Write Tests

File: [libs/next_gen_ui_mcp/agent_test.py](libs/next_gen_ui_mcp/agent_test.py)

Add comprehensive test cases:

Test 3.1: YAML config enables/disables tools

• Create config with mcp.tools.generate_ui_component.enabled: false
• Initialize NextGenUIMCPServer with config (no enabled_tools param)
• Verify generate_ui_component is disabled, generate_ui_multiple_components is enabled

Test 3.2: CLI/env precedence over YAML

• Create config with mcp.tools.generate_ui_component.enabled: false
• Initialize with enabled_tools=["generate_ui_component"]
• Verify generate_ui_component is enabled (CLI overrides YAML)

Test 3.3: Default behavior (all enabled)

• Initialize with no config and no enabled_tools
• Verify all tools are enabled

Test 3.4: YAML enables subset of tools

• Create config with both tools having explicit enabled: true/false
• Verify correct tools are enabled

Test 3.5: Verify tool actually works/doesn't work

• Test that disabled tool is not listed in MCP server tools
• Test that enabled tool can be called successfully

Testing approach: Use pytest fixtures and existing patterns from agent_test.py

4. Update Documentation

File: [libs/next_gen_ui_mcp/README.md](libs/next_gen_ui_mcp/README.md)

Update section "Configuration Reference" (line ~90)

Add row for YAML config path reference

Update section "YAML configuration" (line ~170)

Expand the example (line 178-190) to include enabled field:

mcp:
  tools:
    generate_ui_component:
      enabled: false  # Disable this tool (default: true)
    generate_ui_multiple_components:
      description: Generate multiple UI components for given user_prompt and input data.\nAlways get fresh data from another tool first.
      enabled: true  # Explicitly enable (optional, default is true)
      argument_descriptions:
        user_prompt: "Original user prompt without any changes, so UI components have necessary context. Do not generate this."

Add explanation of precedence:

**Tool Enabling/Disabling Precedence:**

1. **CLI/Environment** (highest): `--tools` / `MCP_TOOLS` - when specified, overrides YAML
2. **YAML Configuration**: `mcp.tools.<tool_name>.enabled` - controls per-tool enablement
3. **Default** (lowest): All tools enabled

Examples:
- YAML disables `generate_ui_component`, no CLI arg → tool is disabled
- YAML disables `generate_ui_component`, CLI `--tools generate_ui_component` → tool is enabled (CLI wins)
- No YAML, no CLI → all tools enabled (default)

Files to Modify

1. [libs/next_gen_ui_mcp/agent_config.py](libs/next_gen_ui_mcp/agent_config.py) - Add enabled field
2. [libs/next_gen_ui_mcp/agent.py](libs/next_gen_ui_mcp/agent.py) - Implement precedence logic in __init__
3. [libs/next_gen_ui_mcp/agent_test.py](libs/next_gen_ui_mcp/agent_test.py) - Add comprehensive tests
4. [libs/next_gen_ui_mcp/README.md](libs/next_gen_ui_mcp/README.md) - Update documentation

Validation

• All tests pass: pants test libs/next_gen_ui_mcp::
• Format/lint clean: Run pants format check skill
• Existing functionality unchanged when no YAML config used
• CLI/env variables maintain backward compatibility