Fastmail MCP Server

rename_mailbox

Rename an existing mailbox (folder) to a new name. Provide the mailbox ID and new name.

Instructions

Rename an existing mailbox (folder). Use list_mailboxes to find the mailbox ID.

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": {
      "mailboxId": "<mailboxId>",
      "newName": "<newName>"
    },
    "name": "rename_mailbox"
  }
}

Input Schema

Name	Required	Description	Default
`newName`	Yes	The new name for the mailbox
`mailboxId`	Yes	The mailbox ID to rename

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.3.0Aug 2, 2026

TDQS

A3.8/5.0

Behavior2/5

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

With no annotations, the description must disclose behavioral traits. It only states the operation renames an existing mailbox, but does not mention permissions, side effects, or whether renaming affects child folders or references. Minimal behavioral context beyond the core action.

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 concise sentences, front-loaded with the action and object. The second sentence provides a useful pointer to list_mailboxes. No redundant wording.

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 two-parameter tool with no output schema, the description gives the essential info: the operation and a way to obtain the required ID. It lacks details on return values or error cases but is adequate for straightforward invocation.

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 description coverage is 100%, so both parameters are documented in the schema itself. The description adds no extra parameter-level information, warranting the baseline score of 3.

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 uses a specific verb ('Rename') and resource ('existing mailbox (folder)'), clearly distinguishing it from sibling tools like create_mailbox and delete_mailbox. It also explains the synonymous term 'folder' for clarity.

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?

The description explicitly instructs to use list_mailboxes to find the mailbox ID, which is a concrete prerequisite. It does not mention excluded scenarios, but the rename action is unambiguous and the guidance is sufficient.

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