Previous value: -"Publication or creation date as LOC catalogs it: free text, a year, or a full date (e.g., \"c1915 Feb. 19.\", \"1912\")."New value: +"Publication or creation date as LOC catalogs it: free text, a year, or a full date (e.g., \"c1915 Feb. 19.\", \"1912\"). Absent when LOC records only a coded value (\"uuuu\", \"||||\") or none."

Previous value: -"LOC identifier for this result. When is_item is true, pass it to libofcongress_get_item for full metadata. When is_item is false it is a non-item resource (a collection, exhibit, guide, or newspaper page), not a get_item input — open url instead."New value: +"LOC identifier for this result: an item ID, or the bare LCCN of a record whose url is an lccn.loc.gov permalink. When is_item is true, pass it to libofcongress_get_item for full metadata. When is_item is false it is a non-item resource (a collection, exhibit, guide, newspaper page, catalog.loc.gov record, or hdl.loc.gov finding aid), not a get_item input — open url instead."

Previous value: -"True when this result is a catalog item whose id resolves through libofcongress_get_item. False for collections, exhibits, research guides, newspaper pages, and other non-item results, which have no get_item record — follow url instead. Always present on every result."New value: +"True when this result is a catalog item whose id resolves through libofcongress_get_item, including records LOC links by an lccn.loc.gov permalink. False for collections, exhibits, research guides, newspaper pages, catalog.loc.gov records, hdl.loc.gov finding aids, and other non-item results, which have no get_item record — follow url instead. Always present on every result."

Previous value: -"End year for date filter, inclusive (e.g., 1930). Omit for no upper bound."New value: +"End year for date filter, inclusive (e.g., 1930). Omit to run through the current year."

Added value: +{
+  "default": false,
+  "description": "Also return subject_facets and location_facets: LOC's top subject and location terms across every match, with counts — the values the subject and location filters accept. Default false: facets add time to each search, so request them when you need filter values to narrow by.",
+  "type": "boolean"
+}

Previous value: -"Results per page. Default 25, max 100."New value: +"Results per page. Default 25. A page holds at most 100 results: a larger limit (up to 1000) is served as a 100-result page, and page then counts 100-result pages."

Previous value: -100New value: +1000

Previous value: -"Geographic location filter (e.g., \"oklahoma\", \"washington d.c.\"). Lowercase, matches LOC location facets."New value: +"Geographic location filter (e.g., \"oklahoma\", \"washington d.c.\"). Lowercase, matches LOC location facets; location_facets (include_facets) lists values for a search."

Previous value: -"Subject heading filter. Use the exact label from libofcongress_search_subjects results for best precision. Example: \"World War, 1939-1945\"."New value: +"Subject filter: an LCSH heading from libofcongress_search_subjects (e.g., \"World War, 1939-1945\", \"United States--History--Civil War, 1861-1865\") or a subject term from subject_facets (include_facets) or libofcongress_get_item subject_terms (e.g., \"world war\"). LOC indexes headings by their parts, so the value is split at \"--\" into lowercase terms with dates dropped, and an item must carry every term."

Added value: +{
+  "description": "The page size actually served when limit exceeded the per-call cap of 100. Absent when limit was within the cap.",
+  "type": "number"
+}

Added value: +{
+  "description": "The subject terms the subject filter was sent as, all required to match. Absent when no subject filter was given.",
+  "items": {
+    "type": "string"
+  },
+  "type": "array"
+}

Previous value: -"Machine-readable failure mode. Declared by this tool: `invalid_date_range`: date_start is later than date_end. `incompatible_filters`: format and collection_slug were both supplied; each selects a different LOC endpoint, so only one can apply. `collection_not_found`: collection_slug does not resolve to a LOC collection. Reported on page 1; a later page gets the out-of-range notice, since LOC answers both cases the same way there. `rate_limit_exceeded`: LOC API rate limit exceeded; requests are blocked for approximately 1 hour. `server_busy`: More Library of Congress requests are queued on this server than can start within this call's time budget. `request_timed_out`: The Library of Congress did not respond within the 50-second request budget. Other values are possible when a failure originates below the handler."New value: +"Machine-readable failure mode. Declared by this tool: `invalid_date_range`: date_start is later than date_end, or date_start is given alone and is later than the current year. `incompatible_filters`: format and collection_slug were both supplied; each selects a different LOC endpoint, so only one can apply. `collection_not_found`: collection_slug does not resolve to a LOC collection. Reported on page 1; a later page gets the out-of-range notice, since LOC answers both cases the same way there. `rate_limit_exceeded`: LOC API rate limit exceeded; requests are blocked for approximately 1 hour. `server_busy`: More Library of Congress requests are queued on this server than can start within this call's time budget. `request_timed_out`: The Library of Congress did not respond within the 50-second request budget. `upstream_unavailable`: The Library of Congress could not be reached, or answered with an error status, a bot challenge or other HTML page, or an unreadable response instead of its JSON. Other values are possible when a failure originates below the handler."

Previous value: -[
-  "invalid_date_range",
-  "incompatible_filters",
-  "collection_not_found",
-  "rate_limit_exceeded",
-  "server_busy",
-  "request_timed_out"
-]New value: +[
+  "invalid_date_range",
+  "incompatible_filters",
+  "collection_not_found",
+  "rate_limit_exceeded",
+  "server_busy",
+  "request_timed_out",
+  "upstream_unavailable"
+]

Previous value: -"Publication or creation date."New value: +"Publication or creation date as LOC catalogs it: free text, a year, or a full date (e.g., \"c1915 Feb. 19.\", \"1912\")."

Added value: +{
+  "description": "LOC's top location terms across every item matching this search (up to 10), most frequent first. Pass a value as the location filter to narrow the search. Present only when include_facets is true; empty when LOC reports none.",
+  "items": {
+    "additionalProperties": false,
+    "description": "One location facet value.",
+    "properties": {
+      "count": {
+        "description": "Matching items carrying this location term.",
+        "type": "number"
+      },
+      "value": {
+        "description": "The location term, as the location filter accepts it.",
+        "type": "string"
+      }
+    },
+    "required": [
+      "value",
+      "count"
+    ],
+    "type": "object"
+  },
+  "type": "array"
+}

Previous value: -"Recovery hint when results are empty or a page is out of range — echoes applied filters and suggests how to broaden. Absent on successful result pages."New value: +"Recovery hint when results are empty or a page is out of range — echoes applied filters, subject terms and location included, and suggests how to broaden — plus disclosure of a capped limit or of the retrieval ceiling. Absent on ordinary result pages."

Added value: +{
+  "description": "LOC's top subject terms across every item matching this search (up to 10), most frequent first. Pass a value as the subject filter to narrow the search. Present only when include_facets is true; empty when LOC reports none.",
+  "items": {
+    "additionalProperties": false,
+    "description": "One subject facet value.",
+    "properties": {
+      "count": {
+        "description": "Matching items carrying this subject term.",
+        "type": "number"
+      },
+      "value": {
+        "description": "The subject term, as the subject filter accepts it.",
+        "type": "string"
+      }
+    },
+    "required": [
+      "value",
+      "count"
+    ],
+    "type": "object"
+  },
+  "type": "array"
+}