Fastmail MCP Server

remove_labels

Remove specific mailbox labels from an email while preserving all other mailbox assignments.

Instructions

Remove one or more mailbox labels from an email while preserving any other mailbox assignments.

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>",
      "mailboxIds": "<mailboxIds>"
    },
    "name": "remove_labels"
  }
}

Input Schema

Name	Required	Description	Default
`emailId`	Yes	The email ID to update
`mailboxIds`	Yes	Mailbox IDs to remove as labels

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 full burden. It discloses a key behavioral trait (preserving other mailbox assignments) but does not mention idempotency, error handling, or whether removal is permanent. This is adequate for a simple operation but leaves gaps.

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 a single, concise sentence that is front-loaded and contains zero fluff. It efficiently conveys the core purpose and a key constraint.

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?

For a two-parameter tool with no output schema and no annotations, the description covers the purpose and a key behavior but does not mention return values or potential error conditions. This is reasonably complete but could benefit from a note about response or side effects.

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 input schema already provides descriptions for both parameters (emailId and mailboxIds), and schema coverage is 100%. The tool description adds no additional parameter-level information, so the baseline of 3 applies.

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 identifies the action (remove), the resource (mailbox labels from an email), and a specific scope (preserving other mailbox assignments). It distinguishes from add_labels and bulk_remove_labels by focusing on a single email while preserving other assignments.

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

Usage Guidelines2/5

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

No guidance is provided on when to use this tool versus alternatives like bulk_remove_labels or move_email. The description states what it does but does not mention exclusions or preferred contexts.

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