clinicaltrialsgov-mcp-server

Clinicaltrials Get Field Definitions

clinicaltrials_get_field_definitions

Read-onlyIdempotent

Discover and explore field names in the ClinicalTrials.gov data model. Search by keyword, drill into sections, or get an overview to find exact identifiers for queries.

Instructions

Resolve valid field names from the ClinicalTrials.gov data model — the canonical PascalCase identifiers (OverallStatus, EnrollmentCount, LeadSponsorName) accepted by the fields, advancedFilter, and sort parameters of other tools, and as input to clinicaltrials_get_field_values. Select a mode: "search" — keyword search returning ranked matches (pass query, e.g. "enrollment", "sponsor", "adverse events"); "drill" — drill into a specific section by dot-notation path (pass path, e.g. "protocolSection.designModule"); "overview" — top-level summary of all sections (no additional args).

Input Schema

TableJSON Schema

Name	Required	Description
`mode`	Yes	Operation mode. "search" — keyword search (requires `query`); "drill" — drill into a section by path (requires `path`); "overview" — list all top-level sections (no other args needed).
`query`	No	search mode only. Keyword to search field names by — e.g., "enrollment", "sponsor", "adverse events". Returns matching field names ranked by relevance with their full paths and data types.
`path`	No	drill mode only. Dot-notation path to drill into — e.g., "protocolSection.designModule", "protocolSection.eligibilityModule", "resultsSection". Returns the section's individual fields.
`limit`	No	search mode only. Maximum results to return. Default: 20.
`includeIndexedOnly`	No	drill mode only. Only return indexed (searchable) fields. Default: false.

Output Schema

TableJSON Schema

Name	Required	Description
`fields`	Yes	Field definitions, ordered by relevance when mode is "search".
`totalFields`	Yes	Total fields returned.
`resolvedPath`	No	Resolved path when mode is "drill".
`searchQuery`	No	Echo of the keyword used in search mode. Absent for drill and overview.
`truncated`	No	True when the field list was capped by the limit parameter (search mode only).
`shown`	No	Number of fields returned (search mode only).
`cap`	No	The limit cap applied to this search (search mode only).
`notice`	No	Recovery guidance when search mode returns no matches, or a truncation note when results are capped.

Tool Definition Quality

A4.4/5.0

Behavior4/5

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

Annotations already indicate readOnlyHint and idempotentHint. The description adds behavioral context by detailing the three modes and their inputs, which is consistent with non-destructive behavior.

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

Conciseness4/5

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

The description is well-structured, front-loading the core purpose and then detailing modes. It is slightly wordy but each sentence adds value.

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?

Given the tool has an output schema and sibling tools are listed, the description fully covers usage context, mode selection, and relationship to other tools. No gaps remain.

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

Parameters4/5

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

With 100% schema description coverage, the description adds value by providing examples (e.g., 'enrollment', 'sponsor') and clarifying mode-specific requirements beyond the schema's field descriptions.

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?

The description explicitly states the tool resolves valid field names from the ClinicalTrials.gov data model, giving concrete examples like OverallStatus. It distinguishes itself from siblings (e.g., clinicaltrials_search_studies) by focusing on field definitions.

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?

The description clarifies when to use (for field names accepted by other tools' parameters) and explains three modes with specific argument requirements. It doesn't explicitly say when not to use, but context is clear.

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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