Strip unnecessary fields in wpcom_request response

apps/cli/ai/system-prompt.ts

@@ -70,6 +70,8 @@ IMPORTANT: Before doing ANY work, you MUST first check the site's plan by callin
 
 Use \`per_page\` and \`page\` for pagination. Use \`status\` to filter by publish status. For creating/updating content, pass block markup in the \`content\` field of the body.
 
+**IMPORTANT: Minimize response sizes** to avoid exceeding tool output limits. Use \`_fields\` (wp/v2) or \`fields\` (v1.1) query parameters to request only the properties you need and exclude heavy fields like \`content\`. For listing endpoints, fetch with lightweight fields first (e.g. \`_fields=id,slug,title,status\` for wp/v2, or \`fields=ID,name,description,URL\` for v1.1), then fetch individual items by ID when you need the full content. When using \`fields\` with v1.1, always include \`ID\` in the field list.
+
 ## Common WP.com v1.1 Endpoints (set apiNamespace to "")
 
 **Site**: \`GET /\` (site info), \`POST /settings\`

apps/cli/ai/wpcom-tools.ts

@@ -3,6 +3,41 @@ import wpcomFactory from '@studio/common/lib/wpcom-factory';
 import wpcomXhrRequest from '@studio/common/lib/wpcom-xhr-request-factory';
 import { z } from 'zod/v4';
 
+/**
+ * Strips oversized fields from API responses that can't be filtered via query params.
+ *
+ * Special case: the WP.com /sites/{id} endpoint returns a `plan` object whose
+ * `features` sub-field alone is 60K+ characters, which pushes the tool result past
+ * Claude Code's MCP output limit (~100k chars). The v1.1 API doesn't support
+ * sub-field filtering (e.g. `fields=plan.product_slug`), so we can't solve this
+ * via query params. The agent only needs a few plan properties to gate features
+ * since the system prompt hardcodes what each plan tier can do.
+ *
+ * This is NOT a pattern to follow for other endpoints. For general large responses,
+ * the system prompt instructs the agent to use `_fields` (wp/v2) or `fields` (v1.1)
+ * query params to request only the properties it needs.
+ */
+function stripOversizedFields( result: ApiResponse ): ApiResponse {
+	if (
+		result &&
+		typeof result === 'object' &&
+		! Array.isArray( result ) &&
+		result.plan?.features
+	) {
+		return {
+			...result,
+			plan: {
+				product_id: result.plan.product_id,
+				product_slug: result.plan.product_slug,
+				product_name_short: result.plan.product_name_short,
+				expired: result.plan.expired,
+				is_free: result.plan.is_free,
+			},
+		};
+	}
+	return result;
+}
+
 function errorResult( message: string ) {
 	return {
 		content: [ { type: 'text' as const, text: message } ],
@@ -106,7 +141,8 @@ export function createWpcomToolDefinitions( token: string, siteId: number ) {
 						break;
 				}
 
-				return textResult( JSON.stringify( result, null, 2 ) );
+				const compacted = stripOversizedFields( result );
+				return textResult( JSON.stringify( compacted ) );
 			} catch ( error ) {
 				return errorResult(
 					`WP.com API request failed (${ args.method } ${ args.path }): ${ getErrorMessage(