Reduce MCP token usage: truncate Tools/Resources responses and restrict fields/pagination for page/post searches

[igor-adzz]

Problem

• tools/call and resources/read currently serialize full results without limits, pulling heavy fields (post HTML content, large plugin/theme lists, etc.) and quickly burning tokens in Claude.
• Page/post searches via REST aliases (/wp/v2/pages, /wp/v2/posts) do not set _fields/context=embed or enforce small pagination, so large objects are returned.

Affected files: includes/RequestMethodHandlers/ToolsHandler.php, includes/RequestMethodHandlers/ResourcesHandler.php, includes/Tools/McpPostsTools.php, includes/Tools/McpPagesTools.php, optionally includes/Tools/McpCustomPostTypesTools.php.

Proposed solution

• Truncate tool textual responses to 10k characters in ToolsHandler::call_tool (replace direct wp_json_encode($result) with an intermediate variable, clamp, append [truncated]).
• Truncate resource text to 10k characters in ResourcesHandler::read_resource (build $json first, clamp, append [truncated]).
• Add preCallback for wp_posts_search and wp_pages_search in McpPostsTools/McpPagesTools: enforce per_page <= 10 (default 5), set _fields=id,title,excerpt,link,date,slug and context=embed. Optionally, in McpCustomPostTypesTools::search_custom_post_types, map $query->posts to a minimal field set (exclude post_content).

Acceptance criteria

• tools/call responses with long JSON include [truncated] and length ≤ 10,000 bytes.
• resources/read responses are also truncated to 10,000 bytes and include [truncated] when applicable.
• By default, page/post searches return ≤ 10 items and only the listed _fields (no heavy content.rendered).
• Response sizes drop significantly on typical queries (expected 50–90%).

How to test (commands)

• Tools (truncation):

export WP_URL="https://<site>/wp-json/wp/v2/wpmcp"; export JWT="<token>"
curl -s -X POST "$WP_URL" -H "Content-Type: application/json" -H "Accept: application/json, text/event-stream" -H "Authorization: Bearer $JWT" \
-d '{"id":1,"jsonrpc":"2.0","method":"tools/call","params":{"name":"wp_posts_search","arguments":{}}}' \
| jq -r '.content[0].text | length, contains("[truncated]")'

• Resources (truncation):

curl -s -X POST "$WP_URL" -H "Content-Type: application/json" -H "Accept: application/json, text/event-stream" -H "Authorization: Bearer $JWT" \
-d '{"id":2,"jsonrpc":"2.0","method":"resources/read","params":{"uri":"WordPress://site-info"}}' \
| jq -r '.contents[0].text | length, contains("[truncated]")'

• Page/post search (fields/pagination):

curl -s -X POST "$WP_URL" -H "Content-Type: application/json" -H "Accept: application/json, text/event-stream" -H "Authorization: Bearer $JWT" \
-d '{"id":3,"jsonrpc":"2.0","method":"tools/call","params":{"name":"wp_pages_search","arguments":{}}}' \
| jq -r '.[0]? // . | if type=="array" then length else length end'

curl -s -X POST "$WP_URL" -H "Content-Type: application/json" -H "Accept: application/json, text/event-stream" -H "Authorization: Bearer $JWT" \
-d '{"id":4,"jsonrpc":"2.0","method":"tools/call","params":{"name":"wp_pages_search","arguments":{}}}' \
| jq -r '.[0]? // . | if type=="array" then .[0] | keys|sort else . end'