pubmed-mcp-server

Pubmed Lookup Mesh

pubmed_lookup_mesh

Read-only

Look up Medical Subject Headings (MeSH) descriptors by name or free-text term to get scope notes, tree numbers, entry terms, and paginated results.

Instructions

Search and explore the MeSH (Medical Subject Headings) controlled vocabulary. Returns descriptor records with tree numbers, scope notes, and entry terms, plus pagination via offset for paging past the maxResults cap.

Input Schema

TableJSON Schema

Name	Required	Description
`query`	Yes	MeSH descriptor name or free-text term to look up. Must carry a term: a blank or whitespace-only value is rejected rather than searched.
`offset`	No	Result offset for pagination (0-based). Pass the `nextOffset` from the previous response to get the following page; the exact-descriptor match is pinned to the first page only.
`maxResults`	No	Maximum results
`includeDetails`	No	Fetch full MeSH records (scope notes, tree numbers, entry terms)

Output Schema

TableJSON Schema

Name	Required	Description
`error`	No	Present when the call failed. Absent on success.
`query`	No	Original search query
`notice`	No	Optional guidance when no descriptors matched or the offset overshot the result set — suggests spell-check, free-text search, or resetting the offset. Absent on successful result pages.
`offset`	No	Result offset this page was read from
`results`	No	Matching MeSH records
`nextOffset`	No	Offset to request for the next page. Omitted when this is the last page, so its absence is the end-of-results signal.
`totalCount`	No	Total MeSH descriptors matching the query upstream, before the maxResults cap

Schema Changelog

Changes observed during successful MCP inspections.

Changed3 schema fields changedv2.10.12Sep 11, 2026

changedInput schema / properties / query / description

Previous value: -"MeSH descriptor name or free-text term to look up"New value: +"MeSH descriptor name or free-text term to look up. Must carry a term: a blank or whitespace-only value is rejected rather than searched."

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

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."

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

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"
+]

Changed6 schema fields changedv2.10.4Aug 28, 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": [
+      "query",
+      "offset",
+      "results",
+      "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: `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"
+}

removedOutput schema / required

Removed value: -[
-  "query",
-  "offset",
-  "results",
-  "totalCount"
-]

Changed6 schema fields changedv2.10.2Jul 30, 2026

addedInput schema / properties / offset

Added value: +{
+  "default": 0,
+  "description": "Result offset for pagination (0-based). Pass the `nextOffset` from the previous response to get the following page; the exact-descriptor match is pinned to the first page only.",
+  "maximum": 9007199254740991,
+  "minimum": 0,
+  "type": "integer"
+}

addedOutput schema / properties / nextOffset

Added value: +{
+  "description": "Offset to request for the next page. Omitted when this is the last page, so its absence is the end-of-results signal.",
+  "type": "number"
+}

changedOutput schema / properties / notice / description

Previous value: -"Optional guidance when no descriptors matched — suggests spell-check or free-text search. Absent on successful results."New value: +"Optional guidance when no descriptors matched or the offset overshot the result set — suggests spell-check, free-text search, or resetting the offset. Absent on successful result pages."

addedOutput schema / properties / offset

Added value: +{
+  "description": "Result offset this page was read from",
+  "type": "number"
+}

changedOutput schema / properties / totalCount / description

Previous value: -"Total matching MeSH descriptors"New value: +"Total MeSH descriptors matching the query upstream, before the maxResults cap"

changedOutput schema / required

Previous value: -[
-  "query",
-  "results",
-  "totalCount"
-]New value: +[
+  "query",
+  "offset",
+  "results",
+  "totalCount"
+]

Changed4 schema fields changedv2.9.6Jun 19, 2026

addedOutput schema / properties / results / items / properties / entrezUid

Added value: +{
+  "description": "NCBI Entrez UID for this record — the join key for E-utilities (eSummary/eFetch db=mesh).",
+  "type": "string"
+}

changedOutput schema / properties / results / items / properties / meshId / description

Previous value: -"MeSH descriptor unique identifier"New value: +"Canonical MeSH DescriptorUI (e.g. \"D003924\") — resolves at the MeSH Browser and NLM linked data. Falls back to the raw Entrez UID when a record is not decodable."

changedOutput schema / properties / results / items / properties / treeNumbers / description

Previous value: -"MeSH tree numbers"New value: +"Navigable MeSH tree numbers (e.g. \"D02.078.370.141.450\"). Omitted for supplementary concept records (SCRs), which map to a heading rather than occupying a tree position."

changedOutput schema / properties / results / items / required

Previous value: -[
-  "meshId",
-  "name"
-]New value: +[
+  "meshId",
+  "entrezUid",
+  "name"
+]

Changed2 schema fields changedv2.9.4Jun 12, 2026

addedOutput schema / properties / totalCount

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

changedOutput schema / required

Previous value: -[
-  "query",
-  "results"
-]New value: +[
+  "query",
+  "results",
+  "totalCount"
+]

Addedv2.7.6May 29, 2026
Removedv2.7.4May 24, 2026
Addedv2.3.2Apr 4, 2026

TDQS

A4.3/5.0

Behavior4/5

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

The description adds behavioral details beyond the readOnlyHint/openWorldHint annotations by explaining the return contents and the pagination mechanism for paging past the maxResults cap. No contradictions with the annotations are present.

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?

The description is a single sentence with no filler: it front-loads the action and result type, then adds pagination behavior. Every clause contributes 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?

Given the rich input schema, existing output schema, and readOnly/openWorld annotations, the description is complete for agent selection and invocation. It covers the core use case, return contents, and pagination nuance without needing to restate structured fields.

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 coverage is 100% and each parameter already has a detailed description. The description's mention of pagination and offset restates the schema's own guidance without adding significant new parameter-level meaning, so the baseline of 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?

The description states a specific verb ('Search and explore') and a specific resource ('MeSH controlled vocabulary'), and it names the return payload (descriptor records with tree numbers, scope notes, entry terms). This clearly differentiates it from siblings like pubmed_search_articles or pubmed_lookup_citation.

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 clearly implies this tool is for MeSH vocabulary lookups rather than article or citation searches, which is a distinct use case from the siblings. It does not explicitly name alternatives or state when not to use it, 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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