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owen-nash

Fastmail MCP Server

by owen-nash

list_identities

Retrieve all email addresses configured for sending in your Fastmail account.

Instructions

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

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault

No arguments

Implementation Reference

  • src/index.ts:580-586 (registration)
    Tool registration in ListToolsRequestSchema handler: defines the 'list_identities' tool with no input parameters.
      name: 'list_identities',
      description: 'List sending identities (email addresses that can be used for sending)',
      inputSchema: {
        type: 'object',
        properties: {},
      },
    },
  • Handler in CallToolRequestSchema: calls JmapClient.getIdentities() and returns 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),
          },
        ],
      };
    }
  • Helper method on JmapClient: makes a JMAP Identity/get request and returns the list of 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);
    }
  • Helper that finds the default identity (non-deletable) used when no explicit from address is provided.
    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];
    }
Behavior3/5

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

No annotations provided, so description must carry the burden. It states the tool lists identities but does not disclose behavioral traits such as read-only nature, authentication requirements, or edge cases like empty results.

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, no wasted words, front-loaded with verb and resource.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness5/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Tool is simple with no parameters and no output schema. Description is sufficient to understand the tool's function.

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, so parameter semantics are not needed. Baseline 4 applies per criteria.

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 action (list) and resource (sending identities) with additional context (email addresses for sending). It distinguishes from sibling tools that list other entities like contacts, emails, mailboxes, etc.

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

Usage Guidelines3/5

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

No explicit guidance on when to use this tool versus alternatives. Usage is implied by the tool name and description, but lacks contextual clues 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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