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MadLlama25

Fastmail MCP Server

by MadLlama25

list_mailboxes

List all mailboxes in your Fastmail account to view and manage your email folders, aiding in organization and navigation.

Instructions

List all mailboxes in the Fastmail account

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault

No arguments

Implementation Reference

  • src/index.ts:135-141 (registration)
    Tool 'list_mailboxes' is registered in the ListTools handler with its name, description, and empty input schema.
      name: 'list_mailboxes',
      description: 'List all mailboxes in the Fastmail account',
      inputSchema: {
        type: 'object',
        properties: {},
      },
    },
  • The CallTool handler for 'list_mailboxes' calls client.getMailboxes() and returns the result as JSON.
    case 'list_mailboxes': {
      const mailboxes = await client.getMailboxes();
      return {
        content: [
          {
            type: 'text',
            text: JSON.stringify(mailboxes, null, 2),
          },
        ],
      };
    }
  • The JmapClient.getMailboxes() method sends a JMAP Mailbox/get request to the Fastmail API and returns the list of mailboxes.
    async getMailboxes(): Promise<any[]> {
      const session = await this.getSession();
      
      const request: JmapRequest = {
        using: ['urn:ietf:params:jmap:core', 'urn:ietf:params:jmap:mail'],
        methodCalls: [
          ['Mailbox/get', { accountId: session.accountId }, 'mailboxes']
        ]
      };
    
      const response = await this.makeRequest(request);
      return this.getListResult(response, 0);
    }
  • Input schema for list_mailboxes: empty object (no parameters required).
    inputSchema: {
      type: 'object',
      properties: {},
    },
Behavior4/5

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

With no annotations, the description carries full burden. It clearly indicates a read-only list operation with no destructive effects, but lacks details like authentication or rate limits, which are reasonable for such a simple tool.

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, front-loaded sentence with no wasted words.

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?

Given no parameters and no output schema, the description is mostly complete. It could hint at what the output contains, but it's sufficient for a list operation.

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 has 0 parameters with 100% coverage, so baseline is 3. The description does not need to add parameter info, and it doesn't.

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) and the resource (all mailboxes in the Fastmail account), and it distinguishes itself from sibling tools like 'get_mailbox_stats' which require a specific mailbox ID.

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 implicitly tells when to use this tool (when a list of all mailboxes is needed), but it does not explicitly mention alternatives or provide when-not-to-use guidance.

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

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