Fastmail MCP Server

get_identities

List all sender identities (email addresses) available for sending emails from your Fastmail account.

Instructions

List all sender identities (email addresses) available for sending emails

Tool call template

This tool declares no required parameters. Add optional parameters from the input schema as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {},
    "name": "get_identities"
  }
}

Input Schema

Name	Required	Description	Default
No arguments

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.3.0Aug 2, 2026

TDQS

A4/5.0

Behavior3/5

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

With no annotations, the description carries the full burden. 'List all' communicates a read-only enumeration, but it does not disclose potential caveats such as whether disabled or unverified identities are included, or any rate limits. Minimal behavioral detail beyond the obvious read operation.

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?

A single concise sentence with no wasted words. Front-loaded with the verb and resource, and the parenthetical adds essential clarification without redundancy.

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?

For a simple list tool with no parameters, no output schema, and no annotations, the description adequately explains the tool's function. It could potentially mention return format or sorting, but it is not strictly necessary for such a straightforward operation.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters4/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

The tool has zero parameters, and the schema provides 100% coverage by having no properties. The description adds semantic clarity by defining identities as email addresses, which is useful beyond the empty schema. Baseline for zero params is 4.

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 verb 'List', the resource 'sender identities', and the scope 'all', making it distinct from siblings like list_mailboxes or list_calendars. The parenthetical '(email addresses)' adds specificity.

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

Usage Guidelines3/5

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

The phrase 'available for sending emails' implies the tool is relevant when sending messages, but it does not explicitly contrast with alternatives like list_mailboxes or provide exclusion criteria. Usage context is implied rather than stated.

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