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MadLlama25

Fastmail MCP Server

by MadLlama25

list_identities

List all sending identities associated with your Fastmail account, providing the email addresses you can use as senders.

Instructions

List sending identities (email addresses that can be used for sending)

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault

No arguments

Implementation Reference

  • src/index.ts:576-583 (registration)
    Tool 'list_identities' is registered in the ListToolsRequestSchema handler with its description and empty input schema.
    {
      name: 'list_identities',
      description: 'List sending identities (email addresses that can be used for sending)',
      inputSchema: {
        type: 'object',
        properties: {},
      },
    },
  • Handler for 'list_identities' tool call: initializes the JMAP client and calls client.getIdentities(), returning the result as JSON.
    case 'list_identities': {
      const client = initializeClient();
      const identities = await client.getIdentities();
      
      return {
        content: [
          {
            type: 'text',
            text: JSON.stringify(identities, null, 2),
          },
        ],
      };
    }
  • The getIdentities() method on JmapClient which performs the JMAP Identity/get API call to fetch sending identities.
    async getIdentities(): Promise<any[]> {
      const session = await this.getSession();
      
      const request: JmapRequest = {
        using: ['urn:ietf:params:jmap:core', 'urn:ietf:params:jmap:submission'],
        methodCalls: [
          ['Identity/get', {
            accountId: session.accountId
          }, 'identities']
        ]
      };
    
      const response = await this.makeRequest(request);
      return this.getListResult(response, 0);
    }
  • The getDefaultIdentity() helper method that finds the default identity (the one with mayDelete===false) from the identities list.
    async getDefaultIdentity(): Promise<any> {
      const identities = await this.getIdentities();
      
      // Find the default identity (usually the one that can't be deleted)
      return identities.find((id: any) => id.mayDelete === false) || identities[0];
    }
Behavior2/5

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

No annotations provided, so description carries full burden. Only states basic function, no details on safety (e.g., read-only), permissions, or return behavior beyond listing identities.

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?

Single sentence with no wasted words. Front-loaded information: action and subject.

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?

Adequate for a zero-parameter tool, but lacks usage context to differentiate from sibling list tools. No output schema, but description covers basic purpose.

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?

Input schema has zero parameters, baseline is 4 per guidelines. Description adds meaning by explaining what identities are listed (sending email addresses).

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?

Description clearly states the tool lists sending identities, specifically email addresses for sending. This distinguishes it from sibling list tools like list_contacts or list_emails.

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 on when to use this tool versus alternatives. Lacks when-not or exclusion criteria. Agent must infer usage from the name and description alone.

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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