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owen-nash

Fastmail MCP Server

by owen-nash

list_mailboxes

Retrieve a complete list of all mailboxes from your Fastmail account to view and manage email folders.

Instructions

List all mailboxes in the Fastmail account

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault

No arguments

Implementation Reference

  • The switch-case handler for 'list_mailboxes' tool call. Calls client.getMailboxes() and returns the result as JSON.
    switch (name) {
      case 'list_mailboxes': {
        const mailboxes = await client.getMailboxes();
        return {
          content: [
            {
              type: 'text',
              text: JSON.stringify(mailboxes, null, 2),
            },
          ],
        };
      }
  • src/index.ts:136-144 (registration)
    Tool registration for 'list_mailboxes' in the ListToolsRequestSchema handler. Defines name, description, and empty inputSchema.
    tools: [
      {
        name: 'list_mailboxes',
        description: 'List all mailboxes in the Fastmail account',
        inputSchema: {
          type: 'object',
          properties: {},
        },
      },
  • The getMailboxes() method on JmapClient that executes the JMAP Mailbox/get API call 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);
    }
Behavior2/5

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

No annotations are provided, and the description does not disclose any behavioral traits beyond listing, such as read-only nature, rate limits, or pagination.

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 redundancy. Every word is necessary.

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 tool with no parameters and no output schema, the description adequately informs the agent of the tool's purpose, though it omits mention of the return format or structure.

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 with 100% schema coverage. The baseline is 4 as per rubric, and no additional description is needed.

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 'mailboxes' with scope 'all'. It distinguishes from sibling tools like list_emails or list_contacts.

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?

The description provides no guidance on when to use this tool versus alternatives, nor any preconditions or exclusions.

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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