Fastmail MCP Server

search_contacts

Find contacts by name, email, or other criteria and retrieve a summary list of matching contacts from your Fastmail address book.

Instructions

Search contacts by name, email, or other criteria. Returns a summary list of matching contacts.

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": "search_contacts"
  }
}

Input Schema

Name	Required	Description
`email`	No	Filter by email address
`limit`	No	Maximum number of contacts to return (default 50, max 100)
`query`	No	Text search query to match against contact names and emails
`addressBookId`	No	Filter to a specific address book ID from list_address_books

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.3.0Aug 2, 2026

TDQS

A3.5/5.0

Behavior3/5

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

With no annotations, the description carries the burden of behavioral disclosure. It indicates a summary list is returned, but it does not explain search semantics (e.g., case sensitivity, default address book, pagination) or explicitly state that it is read-only.

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 consists of two short, front-loaded sentences that efficiently convey the tool's purpose and output. Every word contributes to understanding without fluff.

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?

The description gives a high-level overview and return type, but without an output schema, it lacks detail on result structure, pagination, and default search scope. The schema covers parameter semantics, but the overall description is minimal for an agent to fully understand invocation behavior.

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 already documents all four parameters with descriptions (100% coverage), and the description only restates the 'name/email/criteria' concept without adding operational detail. The baseline score of 3 is appropriate.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool searches contacts by name, email, or other criteria and returns a summary list. It is specific and distinct from sibling tools like get_contact, though it does not explicitly contrast with them.

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 description implies usage for finding contacts by search criteria, but it does not provide explicit guidance on when to use this instead of get_contact or list_address_books, nor does it mention exclusions or prerequisites.

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