Add Select API Support to MCP Plugin Find Tools

[jhb-dev]

Summary

Add support for Payload's select API to the MCP plugin's findResourceTool, enabling MCP clients to request only specific fields from documents. This would significantly reduce token usage in LLM interactions.

Problem

Currently, the MCP plugin's find tools (find{CollectionName}) always return complete documents with all fields populated. When an MCP client only needs specific fields (e.g., fetching just the titles of all pages), the entire document payload is still returned and transmitted.

For example, if a user prompts: "List the titles of all blog posts"

The MCP client currently receives:

{
  "id": "123",
  "title": "My Blog Post",
  "slug": "my-blog-post",
  "content": "... potentially thousands of characters of rich text ...",
  "author": { ... nested author object ... },
  "categories": [ ... array of categories ... ],
  "meta": { ... SEO metadata ... },
  "createdAt": "2024-01-01T00:00:00.000Z",
  "updatedAt": "2024-01-01T00:00:00.000Z"
}

When all that's needed is:

{
  "id": "123",
  "title": "My Blog Post"
}

This wastes tokens on both the request context and the response, increasing costs and potentially hitting context limits faster.

Proposed Solution

Add a select parameter to the findResources tool schema that accepts a JSON string representing the select query, following Payload's existing Select API.

Benefits

1. Token Savings: Significant reduction in tokens when only specific fields are needed
2. Faster Responses: Less data to serialize and transmit
3. Cost Reduction: Lower API costs for LLM providers that charge by token
4. Better Context Management: More room for actual conversation context instead of unused data
5. Consistency: Aligns MCP plugin capabilities with Payload's REST and Local APIs

Example Usage

MCP tool call to get only titles and slugs of pages:

{
  "tool": "findPages",
  "arguments": {
    "limit": 50,
    "select": "{\"title\": true, \"slug\": true}"
  }
}

Response:

{
  "docs": [
    { "id": "1", "title": "Home", "slug": "home" },
    { "id": "2", "title": "About", "slug": "about" },
    { "id": "3", "title": "Contact", "slug": "contact" }
  ],
  "totalDocs": 3,
  "page": 1,
  "totalPages": 1
}

Additional Considerations

• Consider adding depth parameter to findResources as well, which would complement select for controlling relationship population