Gmail MCP Server

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get_attachment

Download an email attachment by providing the message ID and attachment ID. Returns base64-encoded content and metadata.

Instructions

Download an email attachment by message ID and attachment ID. Returns base64-encoded content with metadata. Use get_email first to find attachment IDs.

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": {
      "messageId": "<messageId>",
      "attachmentId": "<attachmentId>"
    },
    "name": "get_attachment"
  }
}

Input Schema

Name	Required	Description	Default
`messageId`	Yes	Gmail message ID that contains the attachment
`attachmentId`	Yes	Attachment ID from the get_email response

Schema Changelog

Changes observed during successful MCP inspections.

First observedv2.0.0Jun 21, 2026

TDQS

A3.7/5.0

Behavior2/5

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

No annotations provided, so description must bear full burden. Mentions return format (base64-encoded with metadata) but omits permissions, rate limits, or size constraints.

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, front-loaded with action and return type, followed by a concise usage instruction. No wasted words.

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

Completeness3/5

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

Lacks output schema so description should detail return values; mentions base64 content and metadata but not specifics (e.g., metadata fields, error cases). Adequate but not rich.

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 covers both parameters with clear descriptions; description adds minimal extra meaning beyond what schema provides (e.g., 'by message ID and attachment ID').

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 specific verb 'Download' and resource 'email attachment', clearly distinguishes from siblings like get_email by focusing on attachment retrieval.

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 instructs to use get_email first to find attachment IDs, providing clear context for correct usage.

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