Medical Terminologies MCP

ATC Class Members

atc_members

Read-onlyIdempotent

Lists all drug substances under any ATC code, from broad therapeutic classes to individual agents. Use it to identify drugs sharing a pharmacological mechanism or explore an ATC subtree.

Instructions

List the drugs (substances) that belong to an ATC class.

Use this tool to:

Enumerate all members of a therapeutic class (e.g., "A10BA" → metformin, phenformin)
Build a list of drugs sharing a pharmacological mechanism
Explore an ATC subtree at any level

Each member includes its substance-level (7-char) ATC code via source_atc_code, useful for disambiguation when the queried class is at level 1-4. RxNorm's catalog is US-centric; the ATC class names and codes themselves are international.

Input Schema

TableJSON Schema

Name	Required	Description	Default
`atc_code`	Yes	ATC code at any level. Higher levels (1-4) return all member substances; level 5 returns the single substance.

Output Schema

TableJSON Schema

Name	Required	Description
`members`	Yes
`atc_code`	Yes
`provenance`	Yes	Provenance block (contract v1.0): source, URL, data vintage, extraction instant, citation, license
`attribution`	Yes	Canonical source URLs of this response (attribution list)

Schema Changelog

Changes observed during successful MCP inspections.

Changed4 schema fields changedv1.9.1Sep 1, 2026
- removedOutput schema / properties / provenance / properties / data_vintage / anyOf
```
Removed value: -[
-  {
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]
```
- addedOutput schema / properties / provenance / properties / data_vintage / type
```
Added value: +[
+  "string",
+  "null"
+]
```
- removedOutput schema / properties / provenance / properties / license / anyOf
```
Removed value: -[
-  {
-    "type": "string"
-  },
-  {
-    "type": "null"
-  }
-]
```
- addedOutput schema / properties / provenance / properties / license / type
```
Added value: +[
+  "string",
+  "null"
+]
```

Changed3 schema fields changedv1.8.0Aug 10, 2026

addedOutput schema / properties / attribution

Added value: +{
+  "description": "Canonical source URLs of this response (attribution list)",
+  "items": {
+    "type": "string"
+  },
+  "type": "array"
+}

addedOutput schema / properties / provenance

Added value: +{
+  "additionalProperties": false,
+  "description": "Provenance block (contract v1.0): source, URL, data vintage, extraction instant, citation, license",
+  "properties": {
+    "citation": {
+      "description": "Ready-to-use citation/attribution string",
+      "type": "string"
+    },
+    "data_vintage": {
+      "anyOf": [
+        {
+          "type": "string"
+        },
+        {
+          "type": "null"
+        }
+      ],
+      "description": "Version/release of the data as exposed by the source; null when not exposed"
+    },
+    "license": {
+      "anyOf": [
+        {
+          "type": "string"
+        },
+        {
+          "type": "null"
+        }
+      ],
+      "description": "License / legal regime of the data"
+    },
+    "retrieved_at": {
+      "description": "Real instant of the upstream extraction (ISO-8601, UTC). Responses served from cache keep the ORIGINAL fetch instant.",
+      "type": "string"
+    },
+    "source": {
+      "description": "Official upstream source of this data",
+      "type": "string"
+    },
+    "source_url": {
+      "description": "Canonical URL of the source (API base or dataset release)",
+      "type": "string"
+    }
+  },
+  "required": [
+    "source",
+    "source_url",
+    "data_vintage",
+    "retrieved_at",
+    "citation",
+    "license"
+  ],
+  "type": "object"
+}

changedOutput schema / required

Previous value: -[
-  "atc_code",
-  "members"
-]New value: +[
+  "atc_code",
+  "members",
+  "provenance",
+  "attribution"
+]

Changed1 schema field changedv1.5.7Jun 21, 2026
- removedInput schema / additionalProperties
```
Removed value: -false
```
First observedv1.2.1May 11, 2026

TDQS

A4.2/5.0

Behavior4/5

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

Annotations already declare readOnlyHint, openWorldHint, idempotentHint, and non-destructive behavior. The description adds useful behavioral context beyond those flags: the returned members include substance-level 7-char ATC codes via source_atc_code, and it notes the RxNorm catalog is US-centric while ATC identifiers are international.

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 front-loaded with the core purpose, then uses bullets for actionable uses, followed by a concise caveat about output fields and data scope. It is slightly longer than strictly necessary but every sentence adds useful information.

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?

The tool is simple with a single documented parameter, an output schema, and rich annotations. The description covers purpose, usage scenarios, output field details, and data-source caveats, so an agent has enough context to select and invoke the tool correctly.

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?

The schema already fully documents the single atc_code parameter, including the pattern and the behavior at different ATC levels. The description adds a concrete example and emphasizes the substance-level code in results, but the parameter meaning is already well covered by the schema.

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 opens with a specific verb and resource: 'List the drugs (substances) that belong to an ATC class.' It also gives concrete examples and distinguishes the tool's membership-listing purpose from sibling tools like atc_lookup and atc_classify.

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 'Use this tool to' bullets provide clear scenarios: enumerate class members, build lists by pharmacological mechanism, and explore ATC subtrees. It does not explicitly name alternatives or exclusion criteria, but the intended use cases are well communicated.

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