Extension Asset Performance

Reports how each ad EXTENSION performs: sitelinks, callouts, the call button, images, structured snippets, business name and logo — impressions, clicks, cost and conversions per asset.

This answers "which sitelink actually gets clicked" and "how often is the call button used", which no other tool can: list_extension_assets returns configuration only, and rsa_asset_performance covers headlines and descriptions, not extension types. Returns two views: `by_field_type` is the account summary (one row per extension kind) and `assets` is the per-asset detail with each sitelink's own link text or the phone number of a call asset.

`days` is the lookback window. `campaign_id` narrows to one campaign. `field_type` filters to one kind: SITELINK | CALLOUT | CALL | STRUCTURED_SNIPPET | AD_IMAGE | BUSINESS_NAME | BUSINESS_LOGO | PRICE | PROMOTION | MOBILE_APP. `limit` controls this response page (0 = as many rows as safely fit); when `has_more` is true, call again with `page_token=next_page_token` to receive the remaining cached rows without another Google request or credit. Read-only.