add-mcp-tool

name	add-mcp-tool
description	Add a new MCP tool to the Context Keeper server. Use when adding a tool, implementing a new MCP capability, or extending the server's tool surface.

Add MCP Tool

Steps

1. Define the Input Schema

In crates/context-keeper-mcp/src/tools.rs, add a new input struct near the other *Input types:

#[derive(Debug, Deserialize, schemars::JsonSchema)]
pub struct MyToolInput {
    #[schemars(description = "Description shown to MCP clients")]
    pub field: String,
    #[schemars(description = "Optional field with default behavior")]
    pub limit: Option<usize>,
}

Every field needs a #[schemars(description)] — this is what the MCP client sees.

2. Define the Response Type (if needed)

Add a #[derive(Debug, Serialize)] struct if the response has structure beyond a simple string.

3. Implement the Tool Method

Add the method inside the #[tool_router] impl ContextKeeperServer block:

#[tool(description = "One-sentence description for the MCP tool listing")]
async fn my_tool(
    &self,
    Parameters(input): Parameters<MyToolInput>,
) -> Result<String, McpError> {
    // Use self.repo, self.embedder, etc.
    // Map errors with .map_err(|e| McpError::internal_error(format!("...: {e}"), None))
    // Return JSON string
    serde_json::to_string_pretty(&result)
        .map_err(|e| McpError::internal_error(format!("Serialization failed: {e}"), None))
}

4. Update Server Instructions (if significant)

If the tool adds a new capability category, update the instructions string in get_info() at the bottom of tools.rs.

5. Test

cargo build -p context-keeper-mcp
cargo test -p context-keeper-mcp

Then test with an MCP client (Claude Desktop, Cursor, or mcp-cli).

Checklist

• Input struct with schemars::JsonSchema + descriptions on all fields
• #[tool(description = "...")] annotation with clear description
• Errors mapped to McpError variants (not raw anyhow)
• Response is serialized JSON
• Server instructions updated if tool adds new capability