Fastmail MCP Server

get_email_attachments

List attachments on a specific email to see filenames, types, sizes, and blob IDs before downloading. Avoid retrieving the full email body when you only need attachment metadata.

Instructions

List the attachments on a specific email without returning the full email body. Use this when you only need filenames, types, sizes, and blob IDs before calling download_attachment.

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": {
      "emailId": "<emailId>"
    },
    "name": "get_email_attachments"
  }
}

Input Schema

Name	Required	Description	Default
`emailId`	Yes	The email ID whose attachments should be listed

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.3.0Aug 2, 2026

TDQS

A4.5/5.0

Behavior4/5

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

With no annotations, the description carries the burden. It discloses that it avoids returning the full email body and lists the specific attachment fields returned, which is helpful behavioral context. However, it doesn't explicitly state it's a read-only/no-side-effect operation, though that is implied.

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 the core action, and no wasted words. The purpose and usage guidance are packed efficiently.

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?

For a simple single-parameter tool with no output schema, the description adequately states what it returns (filenames, types, sizes, blob IDs) and when to use it. No exclusions or prerequisites are needed.

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 the single parameter (emailId) is clearly described in the schema as 'The email ID whose attachments should be listed.' The description adds no extra parameter semantics, but the baseline of 3 applies since the schema fully handles it.

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 clearly states the action (list attachments) and the specific resource (a specific email), and distinguishes it from sibling tools like download_attachment and get_email by noting it avoids the full email body.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines5/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

Explicitly says when to use this tool ('when you only need filenames, types, sizes, and blob IDs') and names the alternative (download_attachment), giving clear context for tool selection.

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