Previous value: -"Maximum results to return. 0 returns only `totalCount`."New value: +"Maximum results to return, up to 1000 per call; a larger value returns 1000 with a notice naming the next `offset`. 0 returns only `totalCount`."

Previous value: -1000New value: +10000

Previous value: -"PubMed search query (supports full NCBI syntax), sent as written apart from inline formatting tags such as `<i>`, which are removed. Must carry a search term: a value that is blank once markup, bracketed field tags (`[pdat]`), parentheses, and invisible characters such as a zero-width space are disregarded is rejected rather than sent to PubMed."New value: +"PubMed search query (supports full NCBI syntax), sent as written apart from inline formatting tags such as `<i>`, which are removed. Omit it or pass an empty string to search on the filters alone, which needs `author`, `journal`, `meshTerms`, or `publicationTypes`; `all[sb]` selects the whole database for a slice by the other filters. A query given must carry a search term: a value that is blank once markup, bracketed field tags (`[pdat]`), parentheses, and invisible characters such as a zero-width space are disregarded is rejected rather than sent to PubMed."

Removed value: -1

Previous value: -"Fetch brief summaries for top N results (0 = PMIDs only). Above the 50 cap, pass the remaining PMIDs to pubmed_fetch_articles."New value: +"Fetch brief summaries for the top N results (0 = PMIDs only), up to 50 per call; a larger value fetches 50 with a notice. Pass the PMIDs past the cap to pubmed_fetch_articles."

Previous value: -50New value: +500

Removed value: -[
-  "query"
-]

Previous value: -"The term sent to PubMed: the query as written, with a clause appended for each active filter. Only inline formatting tags with no attributes (`<i>`, `<b>`, `<em>`, `<strong>`, `<u>` and their closers) are removed; `&`, `<`, and `>` are sent as written."New value: +"The term sent to PubMed: the query as written, with a clause appended for each active filter, or the filter clauses alone, joined by AND, when no query was given. Only inline formatting tags with no attributes (`<i>`, `<b>`, `<em>`, `<strong>`, `<u>` and their closers) are removed; `&`, `<`, and `>` are sent as written."

Previous value: -"Machine-readable failure mode. Declared by this tool: `queue_full`: The local NCBI request queue shed the call — the queue is full, or the call cannot start before its total deadline (for example behind the cooldown that follows an NCBI 429). `ncbi_unreachable`: NCBI E-utilities failed on every attempt the retry budget allowed — retries ran out, or the next backoff would overrun the total deadline. `ncbi_rate_limited`: NCBI answered HTTP 429 (too many requests) and the call stopped on it — retries ran out, the next backoff would overrun the total deadline, or the Retry-After NCBI named outlasts the time left or the 30-second backoff cap. `ncbi_deadline_exceeded`: The total NCBI request deadline expired before NCBI answered successfully — mid-request, while queued, or during a retry backoff. `ncbi_invalid_response`: NCBI returned a body that could not be parsed (invalid XML/JSON). `ncbi_resource_not_found`: NCBI returned a structured \"not found\" error for the requested ID(s). `blank_query`: The query contains no search term: nothing is left once whitespace and invisible characters such as a zero-width space are disregarded. pubmed_search_articles and pubmed_europepmc_search first decode HTML entities and also disregard markup and parentheses, so `()`, `<b></b>`, and `&nbsp;` hold no term there; pubmed_search_articles also disregards bracketed field tags such as `[pdat]`. `invalid_date_range`: A `dateRange` bound is not a real calendar date — a month outside 01–12, day 00, or a day past the end of its month such as `2023/02/29` — or `minDate` falls after `maxDate` once PubMed expands each partial date: `minDate` from the start of its year or month, `maxDate` to the end. `blank_filter`: An `author`, `journal`, or `language` value, or a `publicationTypes` or `meshTerms` element, holds no term once markup is removed and HTML entities are decoded — only whitespace, invisible characters such as a zero-width space, parentheses, brackets, or double quotes are left, as in `()` or `\"\"` — so its field clause would carry no term. An exactly-empty string is not blank here; it sets no filter. Other values are possible when a failure originates below the handler."New value: +"Machine-readable failure mode. Declared by this tool: `queue_full`: The local NCBI request queue shed the call — the queue is full, or the call cannot start before its total deadline (for example behind the cooldown that follows an NCBI 429). `ncbi_unreachable`: NCBI E-utilities failed on every attempt the retry budget allowed — retries ran out, or the next backoff would overrun the total deadline. `ncbi_rate_limited`: NCBI answered HTTP 429 (too many requests) and the call stopped on it — retries ran out, the next backoff would overrun the total deadline, or the Retry-After NCBI named outlasts the time left or the 30-second backoff cap. `ncbi_deadline_exceeded`: The total NCBI request deadline expired before NCBI answered successfully — mid-request, while queued, or during a retry backoff. `ncbi_invalid_response`: NCBI returned a body that could not be parsed (invalid XML/JSON). `ncbi_resource_not_found`: NCBI returned a structured \"not found\" error for the requested ID(s). `blank_query`: The query contains no search term: nothing is left once whitespace and invisible characters such as a zero-width space are disregarded. pubmed_search_articles and pubmed_europepmc_search first decode HTML entities and also disregard markup and parentheses, so `()`, `<b></b>`, and `&nbsp;` hold no term there; pubmed_search_articles also disregards bracketed field tags such as `[pdat]`. On pubmed_search_articles an exactly-empty `query` is not blank: it means no query, and the search runs on its filters. `invalid_date_range`: A `dateRange` bound is not a real calendar date — a month outside 01–12, day 00, or a day past the end of its month such as `2023/02/29` — or `minDate` falls after `maxDate` once PubMed expands each partial date: `minDate` from the start of its year or month, `maxDate` to the end. `blank_filter`: An `author`, `journal`, or `language` value, or a `publicationTypes` or `meshTerms` element, holds no term once markup is removed and HTML entities are decoded — only whitespace, invisible characters such as a zero-width space, parentheses, brackets, or double quotes are left, as in `()` or `\"\"` — so its field clause would carry no term. An exactly-empty string is not blank here; it sets no filter. `no_search_term`: No `query` is given — it is omitted or an empty string — and no subject filter (`author`, `journal`, `meshTerms`, or `publicationTypes`) carries a term. `dateRange`, `language`, `species`, `hasAbstract`, and `freeFullText` narrow a search without saying what it is for, so they cannot run one alone. Other values are possible when a failure originates below the handler."

Previous value: -[
-  "queue_full",
-  "ncbi_unreachable",
-  "ncbi_rate_limited",
-  "ncbi_deadline_exceeded",
-  "ncbi_invalid_response",
-  "ncbi_resource_not_found",
-  "blank_query",
-  "invalid_date_range",
-  "blank_filter"
-]New value: +[
+  "queue_full",
+  "ncbi_unreachable",
+  "ncbi_rate_limited",
+  "ncbi_deadline_exceeded",
+  "ncbi_invalid_response",
+  "ncbi_resource_not_found",
+  "blank_query",
+  "invalid_date_range",
+  "blank_filter",
+  "no_search_term"
+]

Previous value: -"Optional guidance when the result set does not reflect what was asked for — a field tag PubMed ignored, a phrase it matched nothing for, a dateRange dropped for having one bound, no matches at all, or paging past the end. Absent when nothing applies."New value: +"Optional guidance when the result set does not reflect what was asked for — a field tag PubMed ignored, a phrase it matched nothing for, a dateRange dropped for having one bound, no matches at all, paging past the end, or a `maxResults` or `summaryCount` past its per-call cap, served at the cap. Absent when nothing applies."

Previous value: -"Original query"New value: +"Original query; empty when the search ran on the filters alone"

Previous value: -"PubMed search query (supports full NCBI syntax). Must carry a search term: a value that is blank once markup, bracketed field tags (`[pdat]`), parentheses, and invisible characters such as a zero-width space are disregarded is rejected rather than sent to PubMed."New value: +"PubMed search query (supports full NCBI syntax), sent as written apart from inline formatting tags such as `<i>`, which are removed. Must carry a search term: a value that is blank once markup, bracketed field tags (`[pdat]`), parentheses, and invisible characters such as a zero-width space are disregarded is rejected rather than sent to PubMed."

Previous value: -"Filter by species"New value: +"Filter by species: `humans` adds `humans[MeSH Terms]`, `animals` adds `\"animals\"[mh:noexp]` (animals other than humans; a record indexed for both stays in). Both match only records with MEDLINE species indexing, which preprints and ahead-of-print citations lack."

Previous value: -"Normalized filter values that were applied to the PubMed query"New value: +"Filter values applied to the PubMed query, as sent: each text value as written, formatting tags removed, and dates in YYYY/MM/DD form"

Previous value: -"Species filter applied to the search"New value: +"Species filter applied to the search: `humans` as `humans[MeSH Terms]`, `animals` as `\"animals\"[mh:noexp]`"

Previous value: -"Sanitized query sent to PubMed after applying all active filters"New value: +"The term sent to PubMed: the query as written, with a clause appended for each active filter. Only inline formatting tags with no attributes (`<i>`, `<b>`, `<em>`, `<strong>`, `<u>` and their closers) are removed; `&`, `<`, and `>` are sent as written."

Previous value: -"End date (YYYY/MM/DD, YYYY/MM, or YYYY); empty string disables this bound. Must be a real calendar date — `2023/02/29` is rejected."New value: +"End date (YYYY/MM/DD, YYYY/MM, or YYYY). Must be a real calendar date — `2023/02/29` is rejected. Leaving it empty drops the whole date range, not just this bound; for no upper bound pass a wide sentinel such as `3000`."

Previous value: -"Start date (YYYY/MM/DD, YYYY/MM, or YYYY); empty string disables this bound. Must be a real calendar date — `2023/02/29` is rejected."New value: +"Start date (YYYY/MM/DD, YYYY/MM, or YYYY). Must be a real calendar date — `2023/02/29` is rejected. Leaving it empty drops the whole date range, not just this bound; for no lower bound pass a wide sentinel such as `1000`."

Previous value: -"Maximum results to return"New value: +"Maximum results to return. 0 returns only `totalCount`."

Previous value: -1New value: +0

Previous value: -"Publication date"New value: +"Publication date as YYYY-MM-DD; a month- or year-only date reads as the first day of that month or year. On an NCBI Bookshelf chapter (`docType` \"chapter\") it is the chapter's own date — its last revision, otherwise its contribution — not the year its book began."

Previous value: -"Filter by author name (e.g. \"Smith J\")"New value: +"Filter by author name (e.g. \"Smith J\"). An empty string applies no filter; a value of only whitespace, invisible characters, markup, parentheses, brackets, or double quotes is rejected."

Previous value: -"Filter by date range. The filter is applied only when both `minDate` and `maxDate` are non-empty; either one empty disables the entire date range."New value: +"Filter by date range. The filter is applied only when both `minDate` and `maxDate` are non-empty; either one empty disables the entire date range. A partial date covers its whole year or month, and a range whose `minDate` falls after its `maxDate` is rejected: `2024/06` to `2024` is valid, `2024/07` to `2024/06/30` is not."

Previous value: -"End date (YYYY/MM/DD, YYYY/MM, or YYYY); empty string disables this bound"New value: +"End date (YYYY/MM/DD, YYYY/MM, or YYYY); empty string disables this bound. Must be a real calendar date — `2023/02/29` is rejected."

Previous value: -"Start date (YYYY/MM/DD, YYYY/MM, or YYYY); empty string disables this bound"New value: +"Start date (YYYY/MM/DD, YYYY/MM, or YYYY); empty string disables this bound. Must be a real calendar date — `2023/02/29` is rejected."

Previous value: -"Filter by journal name"New value: +"Filter by journal name. An empty string applies no filter; a value of only whitespace, invisible characters, markup, parentheses, brackets, or double quotes is rejected."

Previous value: -"Filter by language (e.g. \"english\")"New value: +"Filter by language (e.g. \"english\"). An empty string applies no filter; a value of only whitespace, invisible characters, markup, parentheses, brackets, or double quotes is rejected."

Previous value: -"Filter by MeSH terms. Multiple terms are AND'd — all must match."New value: +"Filter by MeSH terms. Multiple terms are AND'd — all must match. Empty strings are skipped; an element of only whitespace, invisible characters, markup, parentheses, brackets, or double quotes is rejected."

Previous value: -"Filter by publication type (e.g. \"Review\", \"Clinical Trial\", \"Meta-Analysis\"). Multiple values are OR'd — any match qualifies."New value: +"Filter by publication type (e.g. \"Review\", \"Clinical Trial\", \"Meta-Analysis\"). Multiple values are OR'd — any match qualifies. Empty strings are skipped; an element of only whitespace, invisible characters, markup, parentheses, brackets, or double quotes is rejected."

Previous value: -"PubMed search query (supports full NCBI syntax). Must carry a search term: a value that is blank once markup, bracketed field tags (`[pdat]`), and parentheses are removed is rejected rather than sent to PubMed as an empty term."New value: +"PubMed search query (supports full NCBI syntax). Must carry a search term: a value that is blank once markup, bracketed field tags (`[pdat]`), parentheses, and invisible characters such as a zero-width space are disregarded is rejected rather than sent to PubMed."

Previous value: -"Machine-readable failure mode. Declared by this tool: `queue_full`: The local NCBI request queue shed the call — the queue is full, or the call cannot start before its total deadline (for example behind the cooldown that follows an NCBI 429). `ncbi_unreachable`: NCBI E-utilities is unreachable after all retry attempts. `ncbi_deadline_exceeded`: Total request deadline expired before NCBI returned a response. `ncbi_invalid_response`: NCBI returned a body that could not be parsed (invalid XML/JSON). `ncbi_resource_not_found`: NCBI returned a structured \"not found\" error for the requested ID(s). `blank_query`: The query holds no search term once whitespace, and anything the tool strips before searching, are removed — so NCBI would receive a blank term. pubmed_search_articles strips markup, bracketed field tags, and parentheses, so a bare field tag such as `[pdat]` or empty parentheses `()` count as blank there. Other values are possible when a failure originates below the handler."New value: +"Machine-readable failure mode. Declared by this tool: `queue_full`: The local NCBI request queue shed the call — the queue is full, or the call cannot start before its total deadline (for example behind the cooldown that follows an NCBI 429). `ncbi_unreachable`: NCBI E-utilities failed on every attempt the retry budget allowed — retries ran out, or the next backoff would overrun the total deadline. `ncbi_rate_limited`: NCBI answered HTTP 429 (too many requests) and the call stopped on it — retries ran out, the next backoff would overrun the total deadline, or the Retry-After NCBI named outlasts the time left or the 30-second backoff cap. `ncbi_deadline_exceeded`: The total NCBI request deadline expired before NCBI answered successfully — mid-request, while queued, or during a retry backoff. `ncbi_invalid_response`: NCBI returned a body that could not be parsed (invalid XML/JSON). `ncbi_resource_not_found`: NCBI returned a structured \"not found\" error for the requested ID(s). `blank_query`: The query contains no search term: nothing is left once whitespace and invisible characters such as a zero-width space are disregarded. pubmed_search_articles and pubmed_europepmc_search first decode HTML entities and also disregard markup and parentheses, so `()`, `<b></b>`, and `&nbsp;` hold no term there; pubmed_search_articles also disregards bracketed field tags such as `[pdat]`. `invalid_date_range`: A `dateRange` bound is not a real calendar date — a month outside 01–12, day 00, or a day past the end of its month such as `2023/02/29` — or `minDate` falls after `maxDate` once PubMed expands each partial date: `minDate` from the start of its year or month, `maxDate` to the end. `blank_filter`: An `author`, `journal`, or `language` value, or a `publicationTypes` or `meshTerms` element, holds no term once markup is removed and HTML entities are decoded — only whitespace, invisible characters such as a zero-width space, parentheses, brackets, or double quotes are left, as in `()` or `\"\"` — so its field clause would carry no term. An exactly-empty string is not blank here; it sets no filter. Other values are possible when a failure originates below the handler."

Previous value: -[
-  "queue_full",
-  "ncbi_unreachable",
-  "ncbi_deadline_exceeded",
-  "ncbi_invalid_response",
-  "ncbi_resource_not_found",
-  "blank_query"
-]New value: +[
+  "queue_full",
+  "ncbi_unreachable",
+  "ncbi_rate_limited",
+  "ncbi_deadline_exceeded",
+  "ncbi_invalid_response",
+  "ncbi_resource_not_found",
+  "blank_query",
+  "invalid_date_range",
+  "blank_filter"
+]

Previous value: -"PubMed search query (supports full NCBI syntax). Must carry a search term: a value that is blank once markup is stripped is rejected rather than sent to PubMed as an empty term."New value: +"PubMed search query (supports full NCBI syntax). Must carry a search term: a value that is blank once markup, bracketed field tags (`[pdat]`), and parentheses are removed is rejected rather than sent to PubMed as an empty term."

Previous value: -[
-  {
-    "not": {
-      "required": [
-        "error"
-      ]
-    },
-    "required": [
-      "query",
-      "offset",
-      "pmids",
-      "summaries",
-      "searchUrl",
-      "effectiveQuery",
-      "totalCount",
-      "appliedFilters"
-    ]
-  },
-  {
-    "required": [
-      "error"
-    ]
-  }
-]New value: +[
+  {
+    "not": {
+      "required": [
+        "error"
+      ]
+    },
+    "required": [
+      "query",
+      "offset",
+      "pmids",
+      "summaries",
+      "searchUrl",
+      "totalCount",
+      "effectiveQuery",
+      "appliedFilters"
+    ]
+  },
+  {
+    "required": [
+      "error"
+    ]
+  }
+]

Previous value: -"Machine-readable failure mode. Declared by this tool: `queue_full`: The local NCBI request queue shed the call — the queue is full, or the call cannot start before its total deadline (for example behind the cooldown that follows an NCBI 429). `ncbi_unreachable`: NCBI E-utilities is unreachable after all retry attempts. `ncbi_deadline_exceeded`: Total request deadline expired before NCBI returned a response. `ncbi_invalid_response`: NCBI returned a body that could not be parsed (invalid XML/JSON). `ncbi_resource_not_found`: NCBI returned a structured \"not found\" error for the requested ID(s). `blank_query`: The query holds no search term once whitespace, and any markup the tool strips first, are removed — so NCBI would receive a blank term. Other values are possible when a failure originates below the handler."New value: +"Machine-readable failure mode. Declared by this tool: `queue_full`: The local NCBI request queue shed the call — the queue is full, or the call cannot start before its total deadline (for example behind the cooldown that follows an NCBI 429). `ncbi_unreachable`: NCBI E-utilities is unreachable after all retry attempts. `ncbi_deadline_exceeded`: Total request deadline expired before NCBI returned a response. `ncbi_invalid_response`: NCBI returned a body that could not be parsed (invalid XML/JSON). `ncbi_resource_not_found`: NCBI returned a structured \"not found\" error for the requested ID(s). `blank_query`: The query holds no search term once whitespace, and anything the tool strips before searching, are removed — so NCBI would receive a blank term. pubmed_search_articles strips markup, bracketed field tags, and parentheses, so a bare field tag such as `[pdat]` or empty parentheses `()` count as blank there. Other values are possible when a failure originates below the handler."

Previous value: -"Machine-readable failure mode. Declared by this tool: `queue_full`: Local NCBI request queue is at capacity. `ncbi_unreachable`: NCBI E-utilities is unreachable after all retry attempts. `ncbi_deadline_exceeded`: Total request deadline expired before NCBI returned a response. `ncbi_invalid_response`: NCBI returned a body that could not be parsed (invalid XML/JSON). `ncbi_resource_not_found`: NCBI returned a structured \"not found\" error for the requested ID(s). `blank_query`: The query holds no search term once whitespace, and any markup the tool strips first, are removed — so NCBI would receive a blank term. Other values are possible when a failure originates below the handler."New value: +"Machine-readable failure mode. Declared by this tool: `queue_full`: The local NCBI request queue shed the call — the queue is full, or the call cannot start before its total deadline (for example behind the cooldown that follows an NCBI 429). `ncbi_unreachable`: NCBI E-utilities is unreachable after all retry attempts. `ncbi_deadline_exceeded`: Total request deadline expired before NCBI returned a response. `ncbi_invalid_response`: NCBI returned a body that could not be parsed (invalid XML/JSON). `ncbi_resource_not_found`: NCBI returned a structured \"not found\" error for the requested ID(s). `blank_query`: The query holds no search term once whitespace, and any markup the tool strips first, are removed — so NCBI would receive a blank term. Other values are possible when a failure originates below the handler."

Previous value: -"Formatted author string"New value: +"Formatted author string — the first three of the record's own authors, then \"et al.\". On an NCBI Bookshelf chapter these are the chapter's authors; the book's editors are reported separately in `editors`."

Added value: +{
+  "description": "Title of the book an NCBI Bookshelf record belongs to, e.g. \"GeneReviews(®)\". Present instead of `source` on a book record; absent on a journal article.",
+  "type": "string"
+}

Added value: +{
+  "description": "What PubMed classifies this record as: \"chapter\" or \"book\" for an NCBI Bookshelf record, \"citation\" for an ordinary journal article. Absent when PubMed supplies none.",
+  "type": "string"
+}

Added value: +{
+  "description": "Editors of the containing book, kept out of `authors` so they cannot displace the record's own authors. Absent on a journal article and on a book that credits no editors.",
+  "items": {
+    "description": "One editor, \"Surname Initials\" as ESummary renders it",
+    "type": "string"
+  },
+  "type": "array"
+}

Added value: +{
+  "description": "Publisher of the book an NCBI Bookshelf record belongs to. Present only on a book record; absent on a journal article.",
+  "type": "string"
+}

Previous value: -"Journal source"New value: +"Journal the article appeared in. Absent on an NCBI Bookshelf record, which has no journal — its venue is in `bookTitle` and `publisherName` instead, and `docType` says which kind of record it is."

Previous value: -"PubMed search query (supports full NCBI syntax)"New value: +"PubMed search query (supports full NCBI syntax). Must carry a search term: a value that is blank once markup is stripped is rejected rather than sent to PubMed as an empty term."

Previous value: -"Machine-readable failure mode. Declared by this tool: `queue_full`: Local NCBI request queue is at capacity. `ncbi_unreachable`: NCBI E-utilities is unreachable after all retry attempts. `ncbi_deadline_exceeded`: Total request deadline expired before NCBI returned a response. `ncbi_invalid_response`: NCBI returned a body that could not be parsed (invalid XML/JSON). `ncbi_resource_not_found`: NCBI returned a structured \"not found\" error for the requested ID(s). Other values are possible when a failure originates below the handler."New value: +"Machine-readable failure mode. Declared by this tool: `queue_full`: Local NCBI request queue is at capacity. `ncbi_unreachable`: NCBI E-utilities is unreachable after all retry attempts. `ncbi_deadline_exceeded`: Total request deadline expired before NCBI returned a response. `ncbi_invalid_response`: NCBI returned a body that could not be parsed (invalid XML/JSON). `ncbi_resource_not_found`: NCBI returned a structured \"not found\" error for the requested ID(s). `blank_query`: The query holds no search term once whitespace, and any markup the tool strips first, are removed — so NCBI would receive a blank term. Other values are possible when a failure originates below the handler."

Previous value: -[
-  "queue_full",
-  "ncbi_unreachable",
-  "ncbi_deadline_exceeded",
-  "ncbi_invalid_response",
-  "ncbi_resource_not_found"
-]New value: +[
+  "queue_full",
+  "ncbi_unreachable",
+  "ncbi_deadline_exceeded",
+  "ncbi_invalid_response",
+  "ncbi_resource_not_found",
+  "blank_query"
+]

Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"

Added value: +false

Previous value: -"http://json-schema.org/draft-07/schema#"New value: +"https://json-schema.org/draft/2020-12/schema"

Added value: +[
+  {
+    "not": {
+      "required": [
+        "error"
+      ]
+    },
+    "required": [
+      "query",
+      "offset",
+      "pmids",
+      "summaries",
+      "searchUrl",
+      "effectiveQuery",
+      "totalCount",
+      "appliedFilters"
+    ]
+  },
+  {
+    "required": [
+      "error"
+    ]
+  }
+]

Added value: +{
+  "additionalProperties": {},
+  "description": "Present when the call failed. Absent on success.",
+  "properties": {
+    "code": {
+      "description": "JSON-RPC error code for this failure.",
+      "maximum": 9007199254740991,
+      "minimum": -9007199254740991,
+      "type": "integer"
+    },
+    "data": {
+      "additionalProperties": {},
+      "properties": {
+        "reason": {
+          "description": "Machine-readable failure mode. Declared by this tool: `queue_full`: Local NCBI request queue is at capacity. `ncbi_unreachable`: NCBI E-utilities is unreachable after all retry attempts. `ncbi_deadline_exceeded`: Total request deadline expired before NCBI returned a response. `ncbi_invalid_response`: NCBI returned a body that could not be parsed (invalid XML/JSON). `ncbi_resource_not_found`: NCBI returned a structured \"not found\" error for the requested ID(s). Other values are possible when a failure originates below the handler.",
+          "examples": [
+            "queue_full",
+            "ncbi_unreachable",
+            "ncbi_deadline_exceeded",
+            "ncbi_invalid_response",
+            "ncbi_resource_not_found"
+          ],
+          "type": "string"
+        },
+        "recovery": {
+          "additionalProperties": {},
+          "description": "Actionable next step for the caller.",
+          "properties": {
+            "hint": {
+              "type": "string"
+            }
+          },
+          "required": [
+            "hint"
+          ],
+          "type": "object"
+        },
+        "retryable": {
+          "description": "Whether retrying may succeed.",
+          "type": "boolean"
+        }
+      },
+      "type": "object"
+    },
+    "message": {
+      "description": "Human-readable description of what went wrong.",
+      "type": "string"
+    }
+  },
+  "required": [
+    "code",
+    "message"
+  ],
+  "type": "object"
+}

Removed value: -[
-  "query",
-  "offset",
-  "pmids",
-  "summaries",
-  "searchUrl",
-  "effectiveQuery",
-  "totalCount",
-  "appliedFilters"
-]

Previous value: -"Result offset for pagination (0-based)"New value: +"Result offset for pagination (0-based). PubMed serves at most the first 9999 records of a result set, so this caps at 9998; narrow the query or add filters to reach anything beyond it."

Previous value: -9007199254740991New value: +9998

Previous value: -"Fetch brief summaries for top N results (0 = PMIDs only)"New value: +"Fetch brief summaries for top N results (0 = PMIDs only). Above the 50 cap, pass the remaining PMIDs to pubmed_fetch_articles."

Previous value: -"Optional guidance when results are empty or paging overshot — e.g. how to broaden filters or reset offset. Absent on successful result pages."New value: +"Optional guidance when the result set does not reflect what was asked for — a field tag PubMed ignored, a phrase it matched nothing for, a dateRange dropped for having one bound, no matches at all, or paging past the end. Absent when nothing applies."

Previous value: -"DOI"New value: +"DOI, cased as NCBI reports it. DOIs are case-insensitive by spec and no case normalization is applied here, so casing can differ from a Europe PMC-sourced `doi` — compare the two case-insensitively."

Added value: +{
+  "description": "Total matching articles",
+  "type": "number"
+}

Removed value: -{
-  "description": "Total matching articles",
-  "type": "number"
-}

Previous value: -[
-  "query",
-  "offset",
-  "pmids",
-  "summaries",
-  "searchUrl",
-  "effectiveQuery",
-  "totalFound",
-  "appliedFilters"
-]New value: +[
+  "query",
+  "offset",
+  "pmids",
+  "summaries",
+  "searchUrl",
+  "effectiveQuery",
+  "totalCount",
+  "appliedFilters"
+]

Previous value: -[
-  "query",
-  "effectiveQuery",
-  "appliedFilters",
-  "totalFound",
-  "offset",
-  "pmids",
-  "summaries",
-  "searchUrl"
-]New value: +[
+  "query",
+  "offset",
+  "pmids",
+  "summaries",
+  "searchUrl",
+  "effectiveQuery",
+  "totalFound",
+  "appliedFilters"
+]

Previous value: -"Filter by date range"New value: +"Filter by date range. The filter is applied only when both `minDate` and `maxDate` are non-empty; either one empty disables the entire date range."

Previous value: -"End date (YYYY/MM/DD, YYYY/MM, or YYYY)"New value: +"End date (YYYY/MM/DD, YYYY/MM, or YYYY); empty string disables this bound"

Previous value: -"Start date (YYYY/MM/DD, YYYY/MM, or YYYY)"New value: +"Start date (YYYY/MM/DD, YYYY/MM, or YYYY); empty string disables this bound"

Added value: +"Brief article summary"

Added value: +"^$|^\\d{4}([/\\-.]\\d{1,2}([/\\-.]\\d{1,2})?)?$"

Added value: +"^$|^\\d{4}([/\\-.]\\d{1,2}([/\\-.]\\d{1,2})?)?$"

Previous value: -"Filter by MeSH terms"New value: +"Filter by MeSH terms. Multiple terms are AND'd — all must match."

Previous value: -"Filter by publication type (e.g. \"Review\", \"Clinical Trial\", \"Meta-Analysis\")"New value: +"Filter by publication type (e.g. \"Review\", \"Clinical Trial\", \"Meta-Analysis\"). Multiple values are OR'd — any match qualifies."

Added value: +{
+  "description": "Optional guidance when results are empty or paging overshot — e.g. how to broaden filters or reset offset. Absent on successful result pages.",
+  "type": "string"
+}

Added value: +{
+  "additionalProperties": false,
+  "description": "Normalized filter values that were applied to the PubMed query",
+  "properties": {
+    "author": {
+      "description": "Author filter applied to the search",
+      "type": "string"
+    },
+    "dateRange": {
+      "additionalProperties": false,
+      "description": "Date range filter applied to the search",
+      "properties": {
+        "dateType": {
+          "description": "Applied date field used for the range filter",
+          "enum": [
+            "pdat",
+            "mdat",
+            "edat"
+          ],
+          "type": "string"
+        },
+        "maxDate": {
+          "description": "Applied maximum date",
+          "type": "string"
+        },
+        "minDate": {
+          "description": "Applied minimum date",
+          "type": "string"
+        }
+      },
+      "required": [
+        "minDate",
+        "maxDate",
+        "dateType"
+      ],
+      "type": "object"
+    },
+    "freeFullText": {
+      "description": "Whether results were restricted to free full-text articles",
+      "type": "boolean"
+    },
+    "hasAbstract": {
+      "description": "Whether results were restricted to articles with abstracts",
+      "type": "boolean"
+    },
+    "journal": {
+      "description": "Journal filter applied to the search",
+      "type": "string"
+    },
+    "language": {
+      "description": "Language filter applied to the search",
+      "type": "string"
+    },
+    "meshTerms": {
+      "description": "MeSH term filters applied to the search",
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
+    "publicationTypes": {
+      "description": "Publication type filters applied to the search",
+      "items": {
+        "type": "string"
+      },
+      "type": "array"
+    },
+    "species": {
+      "description": "Species filter applied to the search",
+      "enum": [
+        "humans",
+        "animals"
+      ],
+      "type": "string"
+    }
+  },
+  "type": "object"
+}

Added value: +{
+  "description": "Sanitized query sent to PubMed after applying all active filters",
+  "type": "string"
+}

Previous value: -[
-  "query",
-  "totalFound",
-  "offset",
-  "pmids",
-  "summaries",
-  "searchUrl"
-]New value: +[
+  "query",
+  "effectiveQuery",
+  "appliedFilters",
+  "totalFound",
+  "offset",
+  "pmids",
+  "summaries",
+  "searchUrl"
+]

Previous value: -"End date (YYYY-MM-DD)"New value: +"End date (YYYY/MM/DD, YYYY/MM, or YYYY)"

Previous value: -"Start date (YYYY-MM-DD)"New value: +"Start date (YYYY/MM/DD, YYYY/MM, or YYYY)"