clinicaltrialsgov-mcp-server

Clinicaltrials Get Field Values

clinicaltrials_get_field_values

Read-onlyIdempotent

Discover valid values for ClinicalTrials.gov fields with study counts per value. Use to explore available filter options before building a search — e.g., valid OverallStatus, Phase, InterventionType, StudyType, or LeadSponsorClass values.

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "fields": "<fields>"
    },
    "name": "clinicaltrials_get_field_values"
  }
}

Input Schema

Name	Required	Description	Default
`fields`	Yes	PascalCase leaf piece name(s) to get value statistics for — an empty list is rejected, not treated as "every field". A group of fields (LeadSponsor, ConditionMesh) is refused with its leaf pieces named (LeadSponsorName, ConditionMeshTerm), and a full path as clinicaltrials_get_field_definitions prints it ("protocolSection.statusModule.overallStatus") is read as its piece name. A comma- or pipe-joined string ("Phase,StudyType") is split into separate names. Examples: OverallStatus, Phase, StudyType, Sex, LeadSponsorClass. Use clinicaltrials_get_field_definitions with a query to find more field names.

Output Schema

Name	Required	Description
`error`	No	Present when the call failed. Absent on success.
`notice`	No	Present when a longest value was cut to a preview — names, for each such field, the clinicaltrials_search_studies arguments that return its full text.
`fieldStats`	No	One entry per requested field: canonical path, PascalCase piece name, data type, and the statistics variant that type carries — top values with study counts plus unique/longest for ENUM/STRING, trueCount/falseCount for BOOLEAN, min/max/avg for INTEGER/NUMBER, min/max/formats for DATE.

Schema Changelog

Changes observed during successful MCP inspections.

Changed4 schema fields changedNov 9, 2026

changedInput schema / properties / fields / anyOf

Previous value: -[
-  {
-    "description": "A single PascalCase field name.",
-    "type": "string"
-  },
-  {
-    "description": "Multiple PascalCase field names (at least one required).",
-    "items": {
-      "type": "string"
-    },
-    "type": "array"
-  }
-]New value: +[
+  {
+    "description": "A single PascalCase leaf piece name.",
+    "type": "string"
+  },
+  {
+    "description": "Multiple PascalCase leaf piece names (at least one required).",
+    "items": {
+      "type": "string"
+    },
+    "type": "array"
+  }
+]

changedInput schema / properties / fields / description

Previous value: -"PascalCase field name(s) to get value statistics for — an empty list is rejected, not treated as \"every field\". A comma- or pipe-joined string (\"Phase,StudyType\") is split into separate names. Examples: OverallStatus, Phase, StudyType, Sex, LeadSponsorClass. Use clinicaltrials_get_field_definitions with a query to find more field names."New value: +"PascalCase leaf piece name(s) to get value statistics for — an empty list is rejected, not treated as \"every field\". A group of fields (LeadSponsor, ConditionMesh) is refused with its leaf pieces named (LeadSponsorName, ConditionMeshTerm), and a full path as clinicaltrials_get_field_definitions prints it (\"protocolSection.statusModule.overallStatus\") is read as its piece name. A comma- or pipe-joined string (\"Phase,StudyType\") is split into separate names. Examples: OverallStatus, Phase, StudyType, Sex, LeadSponsorClass. Use clinicaltrials_get_field_definitions with a query to find more field names."

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 requested field name is not a valid PascalCase piece name. `request_too_long`: The fields list makes the request URL longer than ClinicalTrials.gov accepts — a few hundred piece names in one call. `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. `field_invalid`: A requested name is not a field, names a group of fields such as LeadSponsor or ConditionMesh instead of its leaf pieces, or names a leaf whose type ClinicalTrials.gov does not count, such as LocationGeoPoint. `request_too_long`: The fields list makes the request URL longer than ClinicalTrials.gov accepts — a few hundred piece names in one call. `rate_limited`: ClinicalTrials.gov answered HTTP 429 on every attempt, or the call’s time budget ran out after a 429. `retry_deadline_exceeded`: ClinicalTrials.gov did not answer within the call’s time budget, which covers every request, retry, and wait the call makes. `upstream_timeout`: ClinicalTrials.gov answered HTTP 504 (gateway timeout) on every attempt. Other values are possible when a failure originates below the handler."

changedOutput schema / properties / error / properties / data / properties / reason / examples

Previous value: -[
-  "blank_value",
-  "field_invalid",
-  "request_too_long",
-  "rate_limited"
-]New value: +[
+  "blank_value",
+  "field_invalid",
+  "request_too_long",
+  "rate_limited",
+  "retry_deadline_exceeded",
+  "upstream_timeout"
+]

Changed2 schema fields changedNov 3, 2026

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 requested field name is not a valid PascalCase piece name. `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. `field_invalid`: A requested field name is not a valid PascalCase piece name. `request_too_long`: The fields list makes the request URL longer than ClinicalTrials.gov accepts — a few hundred piece names in one call. `rate_limited`: ClinicalTrials.gov returned 429 after retry budget exhausted. Other values are possible when a failure originates below the handler."

changedOutput schema / properties / error / properties / data / properties / reason / examples

Previous value: -[
-  "blank_value",
-  "field_invalid",
-  "rate_limited"
-]New value: +[
+  "blank_value",
+  "field_invalid",
+  "request_too_long",
+  "rate_limited"
+]

Changed6 schema fields changedOct 23, 2026

changedOutput schema / properties / fieldStats / items / properties / longest / properties / length / description

Previous value: -"Its length in characters."New value: +"Full length of the recorded value in characters, even when truncated."

addedOutput schema / properties / fieldStats / items / properties / longest / properties / truncated

Added value: +{
+  "const": true,
+  "description": "True when value is a preview of at most 2,000 characters; absent when value is whole. The notice names the clinicaltrials_search_studies call that returns the full text.",
+  "type": "boolean"
+}

changedOutput schema / properties / fieldStats / items / properties / longest / properties / value / description

Previous value: -"The longest recorded value."New value: +"The longest recorded value — when truncated is true, only a prefix of at most 2,000 characters (1,999 when the cut would split a surrogate pair)."

changedOutput schema / properties / fieldStats / items / properties / uniqueValuesCount / description

Previous value: -"Number of distinct values."New value: +"Number of distinct values, as ClinicalTrials.gov reports it. Free-text STRING fields it does not count (DetailedDescription, EligibilityCriteria) report 0 here alongside uniqueValuesCounted: false — that 0 is not a count. A 0 without the flag means no recorded values."

addedOutput schema / properties / fieldStats / items / properties / uniqueValuesCounted

Added value: +{
+  "const": false,
+  "description": "False when ClinicalTrials.gov did not count distinct values for this field, so the uniqueValuesCount of 0 is not a real count — the field has recorded values (see longest) but no topValues. Absent otherwise.",
+  "type": "boolean"
+}

addedOutput schema / properties / notice

Added value: +{
+  "description": "Present when a longest value was cut to a preview — names, for each such field, the clinicaltrials_search_studies arguments that return its full text.",
+  "type": "string"
+}

Changed1 schema field changedOct 14, 2026

changedInput schema / properties / fields / description

Previous value: -"PascalCase field name(s) to get value statistics for — an empty list is rejected, not treated as \"every field\". Examples: OverallStatus, Phase, StudyType, Sex, LeadSponsorClass. Use clinicaltrials_get_field_definitions with a query to find more field names."New value: +"PascalCase field name(s) to get value statistics for — an empty list is rejected, not treated as \"every field\". A comma- or pipe-joined string (\"Phase,StudyType\") is split into separate names. Examples: OverallStatus, Phase, StudyType, Sex, LeadSponsorClass. Use clinicaltrials_get_field_definitions with a query to find more field names."

Changed7 schema fields changedSep 12, 2026

changedOutput schema / properties / fieldStats / description

Previous value: -"One entry per requested field: canonical path, PascalCase piece name, data type, missing/unique counts, and top values with study counts (or trueCount/falseCount for BOOLEAN fields)."New value: +"One entry per requested field: canonical path, PascalCase piece name, data type, and the statistics variant that type carries — top values with study counts plus unique/longest for ENUM/STRING, trueCount/falseCount for BOOLEAN, min/max/avg for INTEGER/NUMBER, min/max/formats for DATE."

addedOutput schema / properties / fieldStats / items / properties / avg

Added value: +{
+  "description": "Mean of the recorded values. Present for INTEGER/NUMBER fields.",
+  "type": "number"
+}

addedOutput schema / properties / fieldStats / items / properties / formats

Added value: +{
+  "description": "Date patterns this field is recorded in. Present for DATE fields; more than one means the field mixes precisions across studies.",
+  "items": {
+    "description": "A date pattern, e.g. \"yyyy-MM-dd\".",
+    "type": "string"
+  },
+  "type": "array"
+}

addedOutput schema / properties / fieldStats / items / properties / longest

Added value: +{
+  "additionalProperties": false,
+  "description": "Longest recorded value with its length and a study carrying it. Present for STRING fields only.",
+  "properties": {
+    "length": {
+      "description": "Its length in characters.",
+      "type": "number"
+    },
+    "nctId": {
+      "description": "NCT ID of a study carrying it.",
+      "type": "string"
+    },
+    "value": {
+      "description": "The longest recorded value.",
+      "type": "string"
+    }
+  },
+  "required": [
+    "value",
+    "length",
+    "nctId"
+  ],
+  "type": "object"
+}

addedOutput schema / properties / fieldStats / items / properties / max

Added value: +{
+  "anyOf": [
+    {
+      "description": "Largest value of an INTEGER/NUMBER field.",
+      "type": "number"
+    },
+    {
+      "description": "Latest value of a DATE field, at the precision recorded.",
+      "type": "string"
+    }
+  ],
+  "description": "Largest recorded value — a number for INTEGER/NUMBER, a date string for DATE."
+}

addedOutput schema / properties / fieldStats / items / properties / min

Added value: +{
+  "anyOf": [
+    {
+      "description": "Smallest value of an INTEGER/NUMBER field.",
+      "type": "number"
+    },
+    {
+      "description": "Earliest value of a DATE field, at the precision recorded — a partial date such as \"1900-01\" stays partial.",
+      "type": "string"
+    }
+  ],
+  "description": "Smallest recorded value — a number for INTEGER/NUMBER, a date string for DATE."
+}

changedOutput schema / properties / fieldStats / items / properties / multiValued / description

Previous value: -"True when the field is array-typed (a study can carry several values, e.g. Phase, Condition), so the per-value studiesCount buckets sum above the study total. Use to avoid computing a percentage against the corpus."New value: +"True when the field is repeated — array-typed itself (Phase, Condition) or nested under a repeated object (LocationCountry, one per site) — so a study can carry several values and the per-value studiesCount buckets sum above the study total. Use to avoid computing a percentage against the corpus."

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": [
+      "fieldStats"
+    ]
+  },
+  {
+    "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 requested field name is not a valid PascalCase piece name. `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",
+            "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: -[
-  "fieldStats"
-]
```

Changed2 schema fields changedAug 18, 2026

changedInput schema / properties / fields / anyOf

Previous value: -[
-  {
-    "description": "A single PascalCase field name.",
-    "type": "string"
-  },
-  {
-    "description": "Multiple PascalCase field names (at least one required).",
-    "items": {
-      "type": "string"
-    },
-    "minItems": 1,
-    "type": "array"
-  }
-]New value: +[
+  {
+    "description": "A single PascalCase field name.",
+    "type": "string"
+  },
+  {
+    "description": "Multiple PascalCase field names (at least one required).",
+    "items": {
+      "type": "string"
+    },
+    "type": "array"
+  }
+]

changedInput schema / properties / fields / description

Previous value: -"PascalCase field name(s) to get value statistics for. Examples: OverallStatus, Phase, StudyType, Sex, LeadSponsorClass. Use clinicaltrials_get_field_definitions with a query to find more field names."New value: +"PascalCase field name(s) to get value statistics for — an empty list is rejected, not treated as \"every field\". Examples: OverallStatus, Phase, StudyType, Sex, LeadSponsorClass. Use clinicaltrials_get_field_definitions with a query to find more field names."

Changed2 schema fields changedJun 22, 2026

addedOutput schema / properties / fieldStats / items / properties / multiValued

Added value: +{
+  "description": "True when the field is array-typed (a study can carry several values, e.g. Phase, Condition), so the per-value studiesCount buckets sum above the study total. Use to avoid computing a percentage against the corpus.",
+  "type": "boolean"
+}

changedOutput schema / properties / fieldStats / items / properties / topValues / description

Previous value: -"Values ranked by frequency (capped at 250 by the API). Present for ENUM/STRING fields."New value: +"Values ranked by frequency (capped at 250 by the API). Present for ENUM/STRING fields. When multiValued is true, studiesCount sums can exceed the study total."

Changed1 schema field changedJun 14, 2026

changedInput schema / properties / fields / anyOf

Previous value: -[
-  {
-    "description": "A single PascalCase field name.",
-    "type": "string"
-  },
-  {
-    "description": "Multiple PascalCase field names.",
-    "items": {
-      "type": "string"
-    },
-    "type": "array"
-  }
-]New value: +[
+  {
+    "description": "A single PascalCase field name.",
+    "type": "string"
+  },
+  {
+    "description": "Multiple PascalCase field names (at least one required).",
+    "items": {
+      "type": "string"
+    },
+    "minItems": 1,
+    "type": "array"
+  }
+]

Changed1 schema field changedMay 21, 2026

changedOutput schema / properties / fieldStats / description

Previous value: -"Statistics per requested field."New value: +"One entry per requested field: canonical path, PascalCase piece name, data type, missing/unique counts, and top values with study counts (or trueCount/falseCount for BOOLEAN fields)."

Changed2 schema fields changedMay 3, 2026

changedInput schema / properties / fields / anyOf

Previous value: -[
-  {
-    "description": "A single PascalCase piece name.",
-    "type": "string"
-  },
-  {
-    "description": "Multiple PascalCase piece names.",
-    "items": {
-      "type": "string"
-    },
-    "type": "array"
-  }
-]New value: +[
+  {
+    "description": "A single PascalCase field name.",
+    "type": "string"
+  },
+  {
+    "description": "Multiple PascalCase field names.",
+    "items": {
+      "type": "string"
+    },
+    "type": "array"
+  }
+]

changedInput schema / properties / fields / description

Previous value: -"PascalCase piece name(s) to get values for. Common fields: OverallStatus, Phase, StudyType, InterventionType, LeadSponsorClass, Sex, StdAge, DesignAllocation, DesignPrimaryPurpose, DesignMasking."New value: +"PascalCase field name(s) to get value statistics for. Examples: OverallStatus, Phase, StudyType, Sex, LeadSponsorClass. Use clinicaltrials_get_field_definitions with a query to find more field names."

Changed3 schema fields changedApr 24, 2026

changedInput schema / properties / fields / anyOf

Previous value: -[
-  {
-    "type": "string"
-  },
-  {
-    "items": {
-      "type": "string"
-    },
-    "type": "array"
-  }
-]New value: +[
+  {
+    "description": "A single PascalCase piece name.",
+    "type": "string"
+  },
+  {
+    "description": "Multiple PascalCase piece names.",
+    "items": {
+      "type": "string"
+    },
+    "type": "array"
+  }
+]

addedOutput schema / properties / fieldStats / items / description
```
Added value: +"Statistics for a single requested field."
```
addedOutput schema / properties / fieldStats / items / properties / topValues / items / description
```
Added value: +"A value and its study count."
```

Changed1 schema field changedApr 21, 2026

changedOutput schema / properties / fieldStats / items / properties / topValues / description

Previous value: -"Values ranked by frequency. Present for ENUM/STRING fields."New value: +"Values ranked by frequency (capped at 250 by the API). Present for ENUM/STRING fields."

Changed6 schema fields changedMar 28, 2026

addedOutput schema / properties / fieldStats / items / properties / falseCount

Added value: +{
+  "description": "Studies where field is false. Present for BOOLEAN fields.",
+  "type": "number"
+}

addedOutput schema / properties / fieldStats / items / properties / missingStudiesCount

Added value: +{
+  "description": "Number of studies where this field is absent.",
+  "type": "number"
+}

changedOutput schema / properties / fieldStats / items / properties / topValues / description

Previous value: -"Values ranked by frequency."New value: +"Values ranked by frequency. Present for ENUM/STRING fields."

addedOutput schema / properties / fieldStats / items / properties / trueCount

Added value: +{
+  "description": "Studies where field is true. Present for BOOLEAN fields.",
+  "type": "number"
+}

changedOutput schema / properties / fieldStats / items / properties / type / description

Previous value: -"Field data type (ENUM, STRING, DATE, etc.)."New value: +"Field data type (ENUM, BOOLEAN, STRING, DATE, etc.)."

changedOutput schema / properties / fieldStats / items / required

Previous value: -[
-  "field",
-  "piece",
-  "type",
-  "uniqueValuesCount",
-  "topValues"
-]New value: +[
+  "field",
+  "piece",
+  "type"
+]

First observedMar 28, 2026

TDQS

A4.2/5.0

Behavior4/5

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

The annotations already declare readOnlyHint, idempotentHint, and openWorldHint, so the safety profile is covered. The description adds a behavior the annotations do not: each returned value includes a study count, which tells the agent what to expect from the output. It does not mention rate limits or error behavior, but the schema description already covers rejected empty lists and refused group fields.

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?

Two sentences, with the core purpose plus study counts front-loaded, followed by the usage context and concrete examples. There is no redundant or filler wording.

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

Completeness4/5

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

The annotated read-only lookup tool with full schema coverage and an output schema does not need the description to explain return values. Purpose, usage timing, and example fields are all present. The main gap is that the description says nothing about what happens when a field name is invalid, though the schema addresses that.

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?

With 100% schema description coverage, the schema already documents the PascalCase leaf-name format, splitting on commas or pipes, rejection of empty lists, and refusal of group fields. The description's field examples (OverallStatus, Phase, StudyType, Sex, LeadSponsorClass) largely duplicate the schema's own examples and add no new syntax or constraint meaning, so the 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 and resource: "Discover valid values for ClinicalTrials.gov fields with study counts per value." It names concrete field examples (OverallStatus, Phase, InterventionType, StudyType, LeadSponsorClass), which makes it clearly distinguishable from sibling tools such as clinicaltrials_get_field_definitions and clinicaltrials_search_studies.

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?

Explicitly states when to use it: "Use to explore available filter options before building a search." It also says to use clinicaltrials_get_field_definitions to find more field names, which routes the agent to the right sibling. There is no explicit when-not guidance, so it falls short of a 5.

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 Field Values

Tool call template

Input Schema

Output Schema

Schema Changelog

TDQS

Glama MCP Gateway

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