clinicaltrialsgov-mcp-server

Clinicaltrials Get Study Count

clinicaltrials_get_study_count

Read-onlyIdempotent

Get total clinical trial study count from ClinicalTrials.gov matching a query, without fetching study data. Fast and lightweight. Use for quick statistics or to build breakdowns by calling multiple times with different filters (e.g., count by phase, count by status, count recruiting vs completed for a condition).

Input Schema

TableJSON Schema

Name	Required	Description
`query`	No	General free-text search across all fields. Runs the 57-field relevance search ClinicalTrials.gov publishes for this parameter — NCTId, NCTIdAlias, OrgStudyId, SecondaryId, Acronym, BriefTitle, OfficialTitle, Condition, InterventionName, InterventionOtherName, Phase, StdAge, StudyType, BriefSummary, outcome measures and their descriptions, LeadSponsorName, CollaboratorName, the Location* fields, the Design* fields, and the ConditionAncestorTerm/InterventionAncestorTerm MeSH umbrellas — so a hit need not carry your term in the field you had in mind. Plain words plus AND, OR, NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression — those work here as well as in advancedFilter, so AREA[Phase]PHASE2 is accepted in this parameter; a stray bracket fails. `( )` group sub-expressions and work when matched; `,` acts as AND. The dedicated *Query parameters (conditionQuery, interventionQuery, etc.) scope a search to one field.
`titleQuery`	No	Search within study titles and acronyms only. Matches Acronym, BriefTitle, and OfficialTitle. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND.
`phaseFilter`	No	Filter by trial phase. Omit to count all phases — an empty list is rejected, not treated as "no filter". Values: EARLY_PHASE1, PHASE1, PHASE2, PHASE3, PHASE4, NA. Case and spacing variants ("Phase 3", "early phase 1", "Not Applicable") are accepted, and a list or a comma- or pipe-joined string matches any of the phases. Each entry must name a phase — put search expressions (OR, NOT, AREA[…]) in advancedFilter.
`outcomeQuery`	No	Search within outcome measure fields. Matches PrimaryOutcomeMeasure, SecondaryOutcomeMeasure, OtherOutcomeMeasure, and OutcomeMeasureTitle, plus their description counterparts PrimaryOutcomeDescription, SecondaryOutcomeDescription, OtherOutcomeDescription, OutcomeMeasureDescription, and OutcomeMeasurePopulationDescription — so a term appearing only in outcome prose still matches. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND.
`sponsorQuery`	No	Sponsor/collaborator name search. Matches LeadSponsorName, CollaboratorName, and OrgFullName. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND.
`statusFilter`	No	Filter by study status. Omit to count all statuses — an empty list is rejected, not treated as "no filter". Values: RECRUITING, COMPLETED, ACTIVE_NOT_RECRUITING, NOT_YET_RECRUITING, ENROLLING_BY_INVITATION, SUSPENDED, TERMINATED, WITHDRAWN, UNKNOWN, WITHHELD, NO_LONGER_AVAILABLE, AVAILABLE, APPROVED_FOR_MARKETING, TEMPORARILY_NOT_AVAILABLE.
`locationQuery`	No	Location search — city, state, country, or facility name. Matches LocationCity, LocationState, LocationCountry, LocationFacility, and LocationZip; a study matches when any of its sites does. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND.
`advancedFilter`	No	Advanced filter using AREA[FieldName]value syntax. Examples: "AREA[StudyType]INTERVENTIONAL", "AREA[EnrollmentCount]RANGE[100, 1000]", "AREA[Phase]PHASE2 AND AREA[StudyType]INTERVENTIONAL", "(AREA[Phase]PHASE3 OR AREA[Phase]PHASE4) AND AREA[StudyType]INTERVENTIONAL". AND/OR/NOT join complete AREA[FieldName]value expressions; parentheses group them. Call clinicaltrials_get_field_definitions to find AREA[]-compatible field names.
`conditionQuery`	No	Condition/disease-specific search. E.g., "Type 2 Diabetes", "non-small cell lung cancer". Matches Condition, BriefTitle, OfficialTitle, ConditionMeshTerm, ConditionAncestorTerm, Keyword, and NCTId. ConditionAncestorTerm is the MeSH umbrella above the conditions a study itself lists, so results run broader than those lists — a study can match a parent term it never names. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND.
`interventionQuery`	No	Intervention/treatment search. E.g., "pembrolizumab", "cognitive behavioral therapy". Matches InterventionName, InterventionType, ArmGroupType, InterventionOtherName, BriefTitle, OfficialTitle, ArmGroupLabel, InterventionMeshTerm, Keyword, InterventionAncestorTerm, InterventionDescription, and ArmGroupDescription. InterventionAncestorTerm is the MeSH umbrella above the interventions a study itself lists, so results run broader than those lists. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND.
`includeUnknownEnrollment`	No	Include studies whose EnrollmentCount is the upstream "unknown" sentinel (99999999). Excluded by default — the sentinel pollutes RANGE[N, MAX] queries. Set true for data-quality audits.

Output Schema

TableJSON Schema

Name	Required	Description
`error`	No	Present when the call failed. Absent on success.
`notice`	No	Recovery guidance when totalCount is 0 — suggests how to broaden the query or filters.
`totalCount`	No	Total studies matching the query/filters.
`searchCriteria`	No	Echo of active query/filter criteria applied to this count, including sentinelFilterActive when the default unknown-enrollment exclusion is in effect.

Schema Changelog

Changes observed during successful MCP inspections.

Changed2 schema fields changedOct 14, 2026

changedInput schema / properties / phaseFilter / description

Previous value: -"Filter by trial phase. Omit to count all phases — an empty list is rejected, not treated as \"no filter\". Values: EARLY_PHASE1, PHASE1, PHASE2, PHASE3, PHASE4, NA."New value: +"Filter by trial phase. Omit to count all phases — an empty list is rejected, not treated as \"no filter\". Values: EARLY_PHASE1, PHASE1, PHASE2, PHASE3, PHASE4, NA. Case and spacing variants (\"Phase 3\", \"early phase 1\", \"Not Applicable\") are accepted, and a list or a comma- or pipe-joined string matches any of the phases. Each entry must name a phase — put search expressions (OR, NOT, AREA[…]) in advancedFilter."

changedOutput schema / properties / error / properties / data / properties / reason / description

Previous value: -"Machine-readable failure mode. Declared by this tool: `blank_value`: A parameter was supplied with a blank, whitespace-only, or empty-list value. `field_invalid`: A field name in the advanced filter or AREA[] expression is invalid (often a module name instead of a piece name). `enum_invalid`: statusFilter or phaseFilter contains a value ClinicalTrials.gov does not accept. `query_parse_error`: A free-text query or advancedFilter expression uses syntax the upstream Essie parser rejects — typically a `[` or `]` outside an AREA[…] / RANGE[…] expression, an unmatched `(` / `)`, or an unterminated quote in a query/conditionQuery/etc. value. `rate_limited`: ClinicalTrials.gov returned 429 after retry budget exhausted. Other values are possible when a failure originates below the handler."New value: +"Machine-readable failure mode. Declared by this tool: `blank_value`: A parameter was supplied with a blank, whitespace-only, or empty-list value. A phaseFilter entry of only quotes or invisible format characters (zero-width space) is blank. `field_invalid`: A field name in the advanced filter or AREA[] expression is invalid (often a module name instead of a piece name). `enum_invalid`: A phaseFilter entry resolves to none of the six phase values, or statusFilter or an AREA[] expression carries a value ClinicalTrials.gov does not accept. `query_parse_error`: A free-text query or advancedFilter expression uses syntax the upstream Essie parser rejects — typically a `[` or `]` outside an AREA[…] / RANGE[…] expression, an unmatched `(` / `)`, or an unterminated quote in a query/conditionQuery/etc. value. `rate_limited`: ClinicalTrials.gov returned 429 after retry budget exhausted. Other values are possible when a failure originates below the handler."

Changed6 schema fields changedAug 21, 2026

changedInput schema / $schema

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

addedInput schema / additionalProperties
```
Added value: +false
```

changedOutput schema / $schema

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

addedOutput schema / anyOf

Added value: +[
+  {
+    "not": {
+      "required": [
+        "error"
+      ]
+    },
+    "required": [
+      "totalCount"
+    ]
+  },
+  {
+    "required": [
+      "error"
+    ]
+  }
+]

addedOutput schema / properties / 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: `blank_value`: A parameter was supplied with a blank, whitespace-only, or empty-list value. `field_invalid`: A field name in the advanced filter or AREA[] expression is invalid (often a module name instead of a piece name). `enum_invalid`: statusFilter or phaseFilter contains a value ClinicalTrials.gov does not accept. `query_parse_error`: A free-text query or advancedFilter expression uses syntax the upstream Essie parser rejects — typically a `[` or `]` outside an AREA[…] / RANGE[…] expression, an unmatched `(` / `)`, or an unterminated quote in a query/conditionQuery/etc. value. `rate_limited`: ClinicalTrials.gov returned 429 after retry budget exhausted. Other values are possible when a failure originates below the handler.",
+          "examples": [
+            "blank_value",
+            "field_invalid",
+            "enum_invalid",
+            "query_parse_error",
+            "rate_limited"
+          ],
+          "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"
+}

removedOutput schema / required
```
Removed value: -[
-  "totalCount"
-]
```

Changed9 schema fields changedAug 18, 2026

changedInput schema / properties / conditionQuery / description

Previous value: -"Condition/disease-specific search. E.g., \"Type 2 Diabetes\", \"non-small cell lung cancer\". Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND."New value: +"Condition/disease-specific search. E.g., \"Type 2 Diabetes\", \"non-small cell lung cancer\". Matches Condition, BriefTitle, OfficialTitle, ConditionMeshTerm, ConditionAncestorTerm, Keyword, and NCTId. ConditionAncestorTerm is the MeSH umbrella above the conditions a study itself lists, so results run broader than those lists — a study can match a parent term it never names. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND."

changedInput schema / properties / interventionQuery / description

Previous value: -"Intervention/treatment search. E.g., \"pembrolizumab\", \"cognitive behavioral therapy\". Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND."New value: +"Intervention/treatment search. E.g., \"pembrolizumab\", \"cognitive behavioral therapy\". Matches InterventionName, InterventionType, ArmGroupType, InterventionOtherName, BriefTitle, OfficialTitle, ArmGroupLabel, InterventionMeshTerm, Keyword, InterventionAncestorTerm, InterventionDescription, and ArmGroupDescription. InterventionAncestorTerm is the MeSH umbrella above the interventions a study itself lists, so results run broader than those lists. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND."

changedInput schema / properties / locationQuery / description

Previous value: -"Location search — city, state, country, or facility name. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND."New value: +"Location search — city, state, country, or facility name. Matches LocationCity, LocationState, LocationCountry, LocationFacility, and LocationZip; a study matches when any of its sites does. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND."

changedInput schema / properties / outcomeQuery / description

Previous value: -"Search within outcome measure fields. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND."New value: +"Search within outcome measure fields. Matches PrimaryOutcomeMeasure, SecondaryOutcomeMeasure, OtherOutcomeMeasure, and OutcomeMeasureTitle, plus their description counterparts PrimaryOutcomeDescription, SecondaryOutcomeDescription, OtherOutcomeDescription, OutcomeMeasureDescription, and OutcomeMeasurePopulationDescription — so a term appearing only in outcome prose still matches. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND."

changedInput schema / properties / phaseFilter / anyOf

Previous value: -[
-  {
-    "description": "A single phase value.",
-    "type": "string"
-  },
-  {
-    "description": "Multiple phase values (OR).",
-    "items": {
-      "type": "string"
-    },
-    "minItems": 1,
-    "type": "array"
-  }
-]New value: +[
+  {
+    "description": "A single phase value.",
+    "type": "string"
+  },
+  {
+    "description": "Multiple phase values (OR).",
+    "items": {
+      "type": "string"
+    },
+    "type": "array"
+  }
+]

changedInput schema / properties / query / description

Previous value: -"General free-text search across all fields. Plain words plus AND, OR, NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression — those work here as well as in advancedFilter, so AREA[Phase]PHASE2 is accepted in this parameter; a stray bracket fails. `( )` group sub-expressions and work when matched; `,` acts as AND. The dedicated *Query parameters (conditionQuery, interventionQuery, etc.) scope a search to one field."New value: +"General free-text search across all fields. Runs the 57-field relevance search ClinicalTrials.gov publishes for this parameter — NCTId, NCTIdAlias, OrgStudyId, SecondaryId, Acronym, BriefTitle, OfficialTitle, Condition, InterventionName, InterventionOtherName, Phase, StdAge, StudyType, BriefSummary, outcome measures and their descriptions, LeadSponsorName, CollaboratorName, the Location* fields, the Design* fields, and the ConditionAncestorTerm/InterventionAncestorTerm MeSH umbrellas — so a hit need not carry your term in the field you had in mind. Plain words plus AND, OR, NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression — those work here as well as in advancedFilter, so AREA[Phase]PHASE2 is accepted in this parameter; a stray bracket fails. `( )` group sub-expressions and work when matched; `,` acts as AND. The dedicated *Query parameters (conditionQuery, interventionQuery, etc.) scope a search to one field."

changedInput schema / properties / sponsorQuery / description

Previous value: -"Sponsor/collaborator name search. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND."New value: +"Sponsor/collaborator name search. Matches LeadSponsorName, CollaboratorName, and OrgFullName. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND."

changedInput schema / properties / statusFilter / anyOf

Previous value: -[
-  {
-    "description": "A single status value.",
-    "type": "string"
-  },
-  {
-    "description": "Multiple status values (OR).",
-    "items": {
-      "type": "string"
-    },
-    "minItems": 1,
-    "type": "array"
-  }
-]New value: +[
+  {
+    "description": "A single status value.",
+    "type": "string"
+  },
+  {
+    "description": "Multiple status values (OR).",
+    "items": {
+      "type": "string"
+    },
+    "type": "array"
+  }
+]

changedInput schema / properties / titleQuery / description

Previous value: -"Search within study titles and acronyms only. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND."New value: +"Search within study titles and acronyms only. Matches Acronym, BriefTitle, and OfficialTitle. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND."

Changed4 schema fields changedAug 18, 2026

changedInput schema / properties / phaseFilter / anyOf

Previous value: -[
-  {
-    "description": "A single phase value.",
-    "type": "string"
-  },
-  {
-    "description": "Multiple phase values (OR).",
-    "items": {
-      "type": "string"
-    },
-    "type": "array"
-  }
-]New value: +[
+  {
+    "description": "A single phase value.",
+    "type": "string"
+  },
+  {
+    "description": "Multiple phase values (OR).",
+    "items": {
+      "type": "string"
+    },
+    "minItems": 1,
+    "type": "array"
+  }
+]

changedInput schema / properties / phaseFilter / description

Previous value: -"Filter by trial phase. Values: EARLY_PHASE1, PHASE1, PHASE2, PHASE3, PHASE4, NA."New value: +"Filter by trial phase. Omit to count all phases — an empty list is rejected, not treated as \"no filter\". Values: EARLY_PHASE1, PHASE1, PHASE2, PHASE3, PHASE4, NA."

changedInput schema / properties / statusFilter / anyOf

Previous value: -[
-  {
-    "description": "A single status value.",
-    "type": "string"
-  },
-  {
-    "description": "Multiple status values (OR).",
-    "items": {
-      "type": "string"
-    },
-    "type": "array"
-  }
-]New value: +[
+  {
+    "description": "A single status value.",
+    "type": "string"
+  },
+  {
+    "description": "Multiple status values (OR).",
+    "items": {
+      "type": "string"
+    },
+    "minItems": 1,
+    "type": "array"
+  }
+]

changedInput schema / properties / statusFilter / description

Previous value: -"Filter by study status. Values: RECRUITING, COMPLETED, ACTIVE_NOT_RECRUITING, NOT_YET_RECRUITING, ENROLLING_BY_INVITATION, SUSPENDED, TERMINATED, WITHDRAWN, UNKNOWN, WITHHELD, NO_LONGER_AVAILABLE, AVAILABLE, APPROVED_FOR_MARKETING, TEMPORARILY_NOT_AVAILABLE."New value: +"Filter by study status. Omit to count all statuses — an empty list is rejected, not treated as \"no filter\". Values: RECRUITING, COMPLETED, ACTIVE_NOT_RECRUITING, NOT_YET_RECRUITING, ENROLLING_BY_INVITATION, SUSPENDED, TERMINATED, WITHDRAWN, UNKNOWN, WITHHELD, NO_LONGER_AVAILABLE, AVAILABLE, APPROVED_FOR_MARKETING, TEMPORARILY_NOT_AVAILABLE."

Changed7 schema fields changedJul 26, 2026

changedInput schema / properties / conditionQuery / description

Previous value: -"Condition/disease-specific search. E.g., \"Type 2 Diabetes\", \"non-small cell lung cancer\". Plain words plus AND/OR/NOT. `[ ]` are reserved; `( )` group sub-expressions when matched; `,` acts as AND."New value: +"Condition/disease-specific search. E.g., \"Type 2 Diabetes\", \"non-small cell lung cancer\". Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND."

changedInput schema / properties / interventionQuery / description

Previous value: -"Intervention/treatment search. E.g., \"pembrolizumab\", \"cognitive behavioral therapy\". Plain words plus AND/OR/NOT. `[ ]` are reserved; `( )` group sub-expressions when matched; `,` acts as AND."New value: +"Intervention/treatment search. E.g., \"pembrolizumab\", \"cognitive behavioral therapy\". Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND."

changedInput schema / properties / locationQuery / description

Previous value: -"Location search — city, state, country, or facility name. Plain words plus AND/OR/NOT. `[ ]` are reserved; `( )` group sub-expressions when matched; `,` acts as AND."New value: +"Location search — city, state, country, or facility name. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND."

changedInput schema / properties / outcomeQuery / description

Previous value: -"Search within outcome measure fields. Plain words plus AND/OR/NOT. `[ ]` are reserved; `( )` group sub-expressions when matched; `,` acts as AND."New value: +"Search within outcome measure fields. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND."

changedInput schema / properties / query / description

Previous value: -"General free-text search across all fields. Plain words plus AND, OR, NOT. `[ ]` are reserved (advancedFilter AREA[] only); `( )` group sub-expressions and work when matched; `,` acts as AND. For field-scoped searches, use the dedicated *Query parameters (conditionQuery, interventionQuery, etc.) or advancedFilter with AREA[FieldName]value."New value: +"General free-text search across all fields. Plain words plus AND, OR, NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression — those work here as well as in advancedFilter, so AREA[Phase]PHASE2 is accepted in this parameter; a stray bracket fails. `( )` group sub-expressions and work when matched; `,` acts as AND. The dedicated *Query parameters (conditionQuery, interventionQuery, etc.) scope a search to one field."

changedInput schema / properties / sponsorQuery / description

Previous value: -"Sponsor/collaborator name search. Plain words plus AND/OR/NOT. `[ ]` are reserved; `( )` group sub-expressions when matched; `,` acts as AND."New value: +"Sponsor/collaborator name search. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND."

changedInput schema / properties / titleQuery / description

Previous value: -"Search within study titles and acronyms only. Plain words plus AND/OR/NOT. `[ ]` are reserved; `( )` group sub-expressions when matched; `,` acts as AND."New value: +"Search within study titles and acronyms only. Plain words plus AND/OR/NOT. `[ ]` are valid only inside an AREA[FieldName]value or RANGE[min, max] expression, which this parameter accepts; a stray bracket fails. `( )` group sub-expressions when matched; `,` acts as AND."

Changed1 schema field changedJun 14, 2026

changedOutput schema / properties / searchCriteria / description

Previous value: -"Echo of active query/filter criteria applied to this count."New value: +"Echo of active query/filter criteria applied to this count, including sentinelFilterActive when the default unknown-enrollment exclusion is in effect."

Changed7 schema fields changedJun 8, 2026

changedInput schema / properties / conditionQuery / description

Previous value: -"Condition/disease-specific search. E.g., \"Type 2 Diabetes\", \"non-small cell lung cancer\". Plain words plus AND/OR/NOT only — reserved chars: [ ] ( ) ,"New value: +"Condition/disease-specific search. E.g., \"Type 2 Diabetes\", \"non-small cell lung cancer\". Plain words plus AND/OR/NOT. `[ ]` are reserved; `( )` group sub-expressions when matched; `,` acts as AND."

changedInput schema / properties / interventionQuery / description

Previous value: -"Intervention/treatment search. E.g., \"pembrolizumab\", \"cognitive behavioral therapy\". Plain words plus AND/OR/NOT only — reserved chars: [ ] ( ) ,"New value: +"Intervention/treatment search. E.g., \"pembrolizumab\", \"cognitive behavioral therapy\". Plain words plus AND/OR/NOT. `[ ]` are reserved; `( )` group sub-expressions when matched; `,` acts as AND."

changedInput schema / properties / locationQuery / description

Previous value: -"Location search — city, state, country, or facility name. Plain words plus AND/OR/NOT only — reserved chars: [ ] ( ) ,"New value: +"Location search — city, state, country, or facility name. Plain words plus AND/OR/NOT. `[ ]` are reserved; `( )` group sub-expressions when matched; `,` acts as AND."

changedInput schema / properties / outcomeQuery / description

Previous value: -"Search within outcome measure fields. Plain words plus AND/OR/NOT only — reserved chars: [ ] ( ) ,"New value: +"Search within outcome measure fields. Plain words plus AND/OR/NOT. `[ ]` are reserved; `( )` group sub-expressions when matched; `,` acts as AND."

changedInput schema / properties / query / description

Previous value: -"General free-text search across all fields. Plain words plus AND, OR, NOT only — reserved chars `[ ] ( ) ,` will fail. For field-scoped searches, use the dedicated *Query parameters (conditionQuery, interventionQuery, etc.) or advancedFilter with AREA[FieldName]value."New value: +"General free-text search across all fields. Plain words plus AND, OR, NOT. `[ ]` are reserved (advancedFilter AREA[] only); `( )` group sub-expressions and work when matched; `,` acts as AND. For field-scoped searches, use the dedicated *Query parameters (conditionQuery, interventionQuery, etc.) or advancedFilter with AREA[FieldName]value."

changedInput schema / properties / sponsorQuery / description

Previous value: -"Sponsor/collaborator name search. Plain words plus AND/OR/NOT only — reserved chars: [ ] ( ) ,"New value: +"Sponsor/collaborator name search. Plain words plus AND/OR/NOT. `[ ]` are reserved; `( )` group sub-expressions when matched; `,` acts as AND."

changedInput schema / properties / titleQuery / description

Previous value: -"Search within study titles and acronyms only. Plain words plus AND/OR/NOT only — reserved chars: [ ] ( ) ,"New value: +"Search within study titles and acronyms only. Plain words plus AND/OR/NOT. `[ ]` are reserved; `( )` group sub-expressions when matched; `,` acts as AND."

Changed3 schema fields changedJun 2, 2026

addedInput schema / properties / locationQuery

Added value: +{
+  "description": "Location search — city, state, country, or facility name. Plain words plus AND/OR/NOT only — reserved chars: [ ] ( ) ,",
+  "type": "string"
+}

addedInput schema / properties / outcomeQuery

Added value: +{
+  "description": "Search within outcome measure fields. Plain words plus AND/OR/NOT only — reserved chars: [ ] ( ) ,",
+  "type": "string"
+}

addedInput schema / properties / titleQuery

Added value: +{
+  "description": "Search within study titles and acronyms only. Plain words plus AND/OR/NOT only — reserved chars: [ ] ( ) ,",
+  "type": "string"
+}

Changed3 schema fields changedMay 30, 2026

removedOutput schema / properties / noMatchHints

Removed value: -{
-  "description": "Suggestions when no studies match (totalCount is 0).",
-  "items": {
-    "type": "string"
-  },
-  "type": "array"
-}

addedOutput schema / properties / notice

Added value: +{
+  "description": "Recovery guidance when totalCount is 0 — suggests how to broaden the query or filters.",
+  "type": "string"
+}

changedOutput schema / properties / searchCriteria / description

Previous value: -"Echo of query/filter criteria used."New value: +"Echo of active query/filter criteria applied to this count."

Changed1 schema field changedMay 21, 2026

changedInput schema / properties / advancedFilter / description

Previous value: -"Advanced filter using AREA[] syntax. E.g., \"AREA[StudyType]INTERVENTIONAL\", \"AREA[EnrollmentCount]RANGE[100, 1000]\". Combine with AND/OR/NOT and parentheses. Use clinicaltrials_get_field_definitions with a query to find AREA[]-compatible field names."New value: +"Advanced filter using AREA[FieldName]value syntax. Examples: \"AREA[StudyType]INTERVENTIONAL\", \"AREA[EnrollmentCount]RANGE[100, 1000]\", \"AREA[Phase]PHASE2 AND AREA[StudyType]INTERVENTIONAL\", \"(AREA[Phase]PHASE3 OR AREA[Phase]PHASE4) AND AREA[StudyType]INTERVENTIONAL\". AND/OR/NOT join complete AREA[FieldName]value expressions; parentheses group them. Call clinicaltrials_get_field_definitions to find AREA[]-compatible field names."

Changed2 schema fields changedMay 21, 2026

changedInput schema / properties / advancedFilter / description

Previous value: -"Advanced filter using AREA[] Essie syntax. E.g., \"AREA[StudyType]INTERVENTIONAL\", \"AREA[EnrollmentCount]RANGE[100, 1000]\". Combine with AND/OR/NOT and parentheses. Use clinicaltrials_get_field_definitions with a query to find AREA[]-compatible field names."New value: +"Advanced filter using AREA[] syntax. E.g., \"AREA[StudyType]INTERVENTIONAL\", \"AREA[EnrollmentCount]RANGE[100, 1000]\". Combine with AND/OR/NOT and parentheses. Use clinicaltrials_get_field_definitions with a query to find AREA[]-compatible field names."

changedInput schema / properties / query / description

Previous value: -"General free-text search across all fields. Plain words plus AND, OR, NOT only — brackets, parentheses, and commas are reserved by the upstream Essie parser and will fail. For field-scoped searches, use the dedicated *Query parameters (conditionQuery, interventionQuery, etc.) or advancedFilter with AREA[FieldName]value."New value: +"General free-text search across all fields. Plain words plus AND, OR, NOT only — reserved chars `[ ] ( ) ,` will fail. For field-scoped searches, use the dedicated *Query parameters (conditionQuery, interventionQuery, etc.) or advancedFilter with AREA[FieldName]value."

Changed4 schema fields changedMay 21, 2026

changedInput schema / properties / conditionQuery / description

Previous value: -"Condition/disease-specific search. E.g., \"Type 2 Diabetes\", \"non-small cell lung cancer\"."New value: +"Condition/disease-specific search. E.g., \"Type 2 Diabetes\", \"non-small cell lung cancer\". Plain words plus AND/OR/NOT only — reserved chars: [ ] ( ) ,"

changedInput schema / properties / interventionQuery / description

Previous value: -"Intervention/treatment search. E.g., \"pembrolizumab\", \"cognitive behavioral therapy\"."New value: +"Intervention/treatment search. E.g., \"pembrolizumab\", \"cognitive behavioral therapy\". Plain words plus AND/OR/NOT only — reserved chars: [ ] ( ) ,"

changedInput schema / properties / query / description

Previous value: -"General full-text search across all fields."New value: +"General free-text search across all fields. Plain words plus AND, OR, NOT only — brackets, parentheses, and commas are reserved by the upstream Essie parser and will fail. For field-scoped searches, use the dedicated *Query parameters (conditionQuery, interventionQuery, etc.) or advancedFilter with AREA[FieldName]value."

changedInput schema / properties / sponsorQuery / description

Previous value: -"Sponsor/collaborator name search."New value: +"Sponsor/collaborator name search. Plain words plus AND/OR/NOT only — reserved chars: [ ] ( ) ,"

Changed1 schema field changedMay 4, 2026

addedInput schema / properties / includeUnknownEnrollment

Added value: +{
+  "default": false,
+  "description": "Include studies whose EnrollmentCount is the upstream \"unknown\" sentinel (99999999). Excluded by default — the sentinel pollutes RANGE[N, MAX] queries. Set true for data-quality audits.",
+  "type": "boolean"
+}

Changed1 schema field changedMay 3, 2026

changedInput schema / properties / advancedFilter / description

Previous value: -"Advanced filter using AREA[] Essie syntax. E.g., \"AREA[StudyType]INTERVENTIONAL\", \"AREA[EnrollmentCount]RANGE[100, 1000]\". Combine with AND/OR/NOT and parentheses."New value: +"Advanced filter using AREA[] Essie syntax. E.g., \"AREA[StudyType]INTERVENTIONAL\", \"AREA[EnrollmentCount]RANGE[100, 1000]\". Combine with AND/OR/NOT and parentheses. Use clinicaltrials_get_field_definitions with a query to find AREA[]-compatible field names."

Changed2 schema fields changedApr 24, 2026

changedInput schema / properties / phaseFilter / anyOf

Previous value: -[
-  {
-    "type": "string"
-  },
-  {
-    "items": {
-      "type": "string"
-    },
-    "type": "array"
-  }
-]New value: +[
+  {
+    "description": "A single phase value.",
+    "type": "string"
+  },
+  {
+    "description": "Multiple phase values (OR).",
+    "items": {
+      "type": "string"
+    },
+    "type": "array"
+  }
+]

changedInput schema / properties / statusFilter / anyOf

Previous value: -[
-  {
-    "type": "string"
-  },
-  {
-    "items": {
-      "type": "string"
-    },
-    "type": "array"
-  }
-]New value: +[
+  {
+    "description": "A single status value.",
+    "type": "string"
+  },
+  {
+    "description": "Multiple status values (OR).",
+    "items": {
+      "type": "string"
+    },
+    "type": "array"
+  }
+]

Changed5 schema fields changedApr 4, 2026

changedInput schema / properties / advancedFilter / description

Previous value: -"Advanced AREA[] filter expression."New value: +"Advanced filter using AREA[] Essie syntax. E.g., \"AREA[StudyType]INTERVENTIONAL\", \"AREA[EnrollmentCount]RANGE[100, 1000]\". Combine with AND/OR/NOT and parentheses."

changedInput schema / properties / conditionQuery / description

Previous value: -"Condition/disease search."New value: +"Condition/disease-specific search. E.g., \"Type 2 Diabetes\", \"non-small cell lung cancer\"."

changedInput schema / properties / interventionQuery / description

Previous value: -"Intervention/treatment search."New value: +"Intervention/treatment search. E.g., \"pembrolizumab\", \"cognitive behavioral therapy\"."

changedInput schema / properties / query / description

Previous value: -"General full-text search."New value: +"General full-text search across all fields."

changedInput schema / properties / sponsorQuery / description

Previous value: -"Sponsor search."New value: +"Sponsor/collaborator name search."

First observedMar 28, 2026

TDQS

A4.3/5.0

Behavior4/5

Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?

Annotations already establish readOnlyHint, idempotentHint, and openWorldHint, so the safety profile is covered. The description adds real behavioral value beyond that: it returns counts only, fetches no study data, is fast/lightweight, and is designed for repeated calls to assemble breakdowns. Rate limits or pagination are not discussed, but they are largely irrelevant to a count endpoint.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

Three short sentences, front-loaded with the core purpose before the usage guidance. Every sentence earns its place; no repetition of schema or annotation content.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

An output schema exists so return values need not be described, all 11 parameters are documented in the schema, and annotations cover the safety profile. The description supplies the purpose and usage framing an agent needs, leaving nothing essential unaddressed.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is 100% and the parameter descriptions are extremely detailed (search fields, AREA[]/RANGE syntax, enum value lists), so the schema carries nearly all semantic weight. The description only gestures at filters generically ('different filters', 'phase', 'status'), adding no syntax or format detail beyond the schema; baseline 3 applies.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

States a specific verb+resource (get total study count) with explicit scope ('from ClinicalTrials.gov matching a query, without fetching study data'), which cleanly separates it from the sibling clinicaltrials_search_studies that returns study data. An agent can pick this without opening the schema.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Gives clear when-to-use context ('quick statistics', 'build breakdowns by calling multiple times with different filters') with concrete examples (count by phase, count by status, recruiting vs completed). It stops short of explicitly naming a sibling like clinicaltrials_search_studies as the alternative when full records are needed.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

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Clinicaltrials Get Study Count

Input Schema

Output Schema

Schema Changelog

TDQS

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