Ensembl

Lookup Symbol

lookup_symbol

Read-onlyIdempotent

"What's the Ensembl ID for [gene symbol]" / "look up [gene] in Ensembl" / "BRCA1 / TP53 / BRAF Ensembl info" / "find gene [symbol] in [species]" — look up a gene by symbol within a species (e.g. species="human" symbol="BRCA1"). Returns Ensembl gene ID, chromosomal position, biotype, description. Use to convert HGNC gene symbols to Ensembl IDs for genomics workflows.

Example tool call

This call uses example arguments supplied in the tool’s input schema.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "symbol": "BRAF",
      "species": "human"
    },
    "name": "lookup_symbol"
  }
}

Input Schema

Name	Required	Description
`expand`	No
`symbol`	Yes
`species`	Yes	e.g. "human", "mus_musculus"
`assembly`	No	Human genome build: "GRCh38" (the default) or "GRCh37" (= hg19). Coordinates you pass and coordinates you get back are both in this build. Older variant lists, spreadsheets and published tables are usually GRCh37.

Output Schema

Name	Required	Description
`id`	No	Stable gene ID
`end`	No	End coordinate
`start`	No	Start coordinate
`strand`	No	Strand
`biotype`	No	Biotype
`species`	No	Species name
`Transcript`	No	Transcripts (if expand=true)
`description`	No	Gene description
`object_type`	No	Type of object
`display_name`	No	Display name
`assembly_name`	No	Assembly name
`seq_region_name`	No	Chromosome

Schema Changelog

Changes observed during successful MCP inspections.

Changed1 schema field changedSep 7, 2026

addedInput schema / properties / assembly

Added value: +{
+  "description": "Human genome build: \"GRCh38\" (the default) or \"GRCh37\" (= hg19). Coordinates you pass and coordinates you get back are both in this build. Older variant lists, spreadsheets and published tables are usually GRCh37.",
+  "type": "string"
+}

Changed2 schema fields changedMay 27, 2026

addedInput schema / examples

Added value: +[
+  {
+    "species": "human",
+    "symbol": "BRAF"
+  },
+  {
+    "expand": true,
+    "species": "mus_musculus",
+    "symbol": "Braf"
+  }
+]

changedOutput schema / (root)

Previous value: -nullNew value: +{
+  "description": "Gene lookup by symbol result",
+  "properties": {
+    "Transcript": {
+      "description": "Transcripts (if expand=true)",
+      "items": {
+        "type": "object"
+      },
+      "type": "array"
+    },
+    "assembly_name": {
+      "description": "Assembly name",
+      "type": "string"
+    },
+    "biotype": {
+      "description": "Biotype",
+      "type": "string"
+    },
+    "description": {
+      "description": "Gene description",
+      "type": "string"
+    },
+    "display_name": {
+      "description": "Display name",
+      "type": "string"
+    },
+    "end": {
+      "description": "End coordinate",
+      "type": "integer"
+    },
+    "id": {
+      "description": "Stable gene ID",
+      "type": "string"
+    },
+    "object_type": {
+      "description": "Type of object",
+      "type": "string"
+    },
+    "seq_region_name": {
+      "description": "Chromosome",
+      "type": "string"
+    },
+    "species": {
+      "description": "Species name",
+      "type": "string"
+    },
+    "start": {
+      "description": "Start coordinate",
+      "type": "integer"
+    },
+    "strand": {
+      "description": "Strand",
+      "type": "integer"
+    }
+  },
+  "type": "object"
+}

First observedMay 16, 2026

TDQS

A4.2/5.0

Behavior4/5

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

The annotations already signal readOnly, idempotent, openWorld, and non-destructive behavior, and the description does not contradict these. The description clearly indicates the tool returns gene information rather than performing mutations, so an agent can infer it has no side effects. It does not describe error behavior, but that is not required given the annotations.

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 compact and front-loaded, leading with the action and examples before listing returns and use case. It avoids unnecessary detail and every sentence adds useful context, with no redundant or filler content.

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 description names the return fields (Ensembl gene ID, chromosomal position, biotype, description) and the assembly coordinate behavior, which covers the main information an agent needs. It does not enumerate possible outputs or edge cases, but the absence of a full output schema is mitigated by the explicit list of returned 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?

The schema descriptions cover species and assembly well, and symbol is inferable from the tool name and description. However, the 'expand' boolean parameter has no description in the schema or the main description, leaving its meaning ambiguous. With 50% schema description coverage and one entirely unexplained parameter, the description only partially compensates for the gap.

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 action ('look up a gene by symbol within a species'), includes concrete examples (BRCA1, TP53, BRAF), and lists the returned fields. It also identifies the intended use case, converting HGNC gene symbols to Ensembl IDs, making the tool's purpose unmistakable.

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 provides a clear when-to-use directive: 'Use to convert HGNC gene symbols to Ensembl IDs for genomics workflows.' It does not explicitly contrast with sibling tools such as lookup, sequence, or variation, but the stated use case is specific enough for an agent to select it appropriately in most situations.

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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