check_function_availability

Instructions

Implementation Reference

• src/index.ts:959-965 (registration)

  Tool 'check_function_availability' is registered in the ListToolsRequestSchema handler with its description and input schema.

    name: 'check_function_availability',
    description: 'Check which MCP functions are available based on account permissions',
    inputSchema: {
      type: 'object',
      properties: {},
    },
  },

• src/index.ts:1747-1809 (handler)

  Handler for the 'check_function_availability' tool in the CallToolRequestSchema switch statement. It calls client.getSession() to examine JMAP session capabilities and returns a JSON report on which function categories (email, identity, contacts, calendar) are available, including guidance for enabling missing features.

  case 'check_function_availability': {
    const client = initializeClient();
    const session = await client.getSession();
    
    const availability = {
      email: {
        available: true,
        functions: [
          'list_mailboxes', 'list_emails', 'get_email', 'send_email', 'create_draft', 'edit_draft', 'send_draft', 'search_emails',
          'get_recent_emails', 'mark_email_read', 'pin_email', 'delete_email', 'move_email',
          'get_email_attachments', 'download_attachment', 'advanced_search', 'get_thread',
          'get_mailbox_stats', 'get_account_summary', 'bulk_mark_read', 'bulk_pin', 'bulk_move', 'bulk_delete',
          'add_labels', 'remove_labels', 'bulk_add_labels', 'bulk_remove_labels'
        ]
      },
      identity: {
        available: true,
        functions: ['list_identities']
      },
      contacts: {
        available: !!session.capabilities['urn:ietf:params:jmap:contacts'],
        functions: ['list_contacts', 'get_contact', 'search_contacts'],
        note: session.capabilities['urn:ietf:params:jmap:contacts'] ? 
          'Contacts are available' : 
          'Contacts access not available - may require enabling in Fastmail account settings',
        enablementGuide: session.capabilities['urn:ietf:params:jmap:contacts'] ? null : {
          steps: [
            '1. Log into Fastmail web interface',
            '2. Go to Settings → Privacy & Security → Connected Apps & API tokens',
            '3. Check if contacts scope is enabled for your API token',
            '4. If not available, you may need to upgrade your Fastmail plan or contact support'
          ],
          documentation: 'https://www.fastmail.com/help/technical/jmap-api.html'
        }
      },
      calendar: {
        available: !!session.capabilities['urn:ietf:params:jmap:calendars'],
        functions: ['list_calendars', 'list_calendar_events', 'get_calendar_event', 'create_calendar_event'],
        note: session.capabilities['urn:ietf:params:jmap:calendars'] ? 
          'Calendar is available' : 
          'Calendar access not available - may require enabling in Fastmail account settings',
        enablementGuide: session.capabilities['urn:ietf:params:jmap:calendars'] ? null : {
          steps: [
            '1. Log into Fastmail web interface',
            '2. Go to Settings → Privacy & Security → Connected Apps & API tokens',
            '3. Check if calendar scope is enabled for your API token',
            '4. If not available, you may need to upgrade your Fastmail plan or contact support'
          ],
          documentation: 'https://www.fastmail.com/help/technical/jmap-api.html'
        }
      },
      capabilities: Object.keys(session.capabilities)
    };
    
    return {
      content: [
        {
          type: 'text',
          text: JSON.stringify(availability, null, 2),
        },
      ],
    };
  }

• src/jmap-client.ts:72-115 (helper)

  getSession() method on JmapClient fetches the JMAP session from the server, validates URLs, and returns session data including capabilities used by the handler.

  async getSession(): Promise<JmapSession> {
    if (this.session) {
      return this.session;
    }
  
    const response = await fetch(this.auth.getSessionUrl(), {
      method: 'GET',
      headers: this.auth.getAuthHeaders()
    });
  
    if (!response.ok) {
      throw new Error(`Failed to get session: ${response.statusText}`);
    }
  
    const sessionData = await response.json() as any;
  
    // Validate every URL the server hands us before we send the bearer token to it.
    // The downloadUrl/uploadUrl are URL templates with {accountId}/{blobId}/etc.
    // placeholders, so we strip those for parsing and validate origin only.
    const allowUnsafe = this.auth.getAllowUnsafe();
    const stripTemplate = (url: string) => url.replace(/\{[^}]+\}/g, 'x');
    if (typeof sessionData.apiUrl !== 'string') {
      throw new Error('Invalid session response: apiUrl missing');
    }
    validateFastmailUrl(sessionData.apiUrl, 'session.apiUrl', allowUnsafe);
    if (typeof sessionData.downloadUrl === 'string') {
      validateFastmailUrl(stripTemplate(sessionData.downloadUrl), 'session.downloadUrl', allowUnsafe);
    }
    if (typeof sessionData.uploadUrl === 'string') {
      validateFastmailUrl(stripTemplate(sessionData.uploadUrl), 'session.uploadUrl', allowUnsafe);
    }
  
    this.session = {
      apiUrl: sessionData.apiUrl,
      accountId: sessionData.primaryAccounts?.['urn:ietf:params:jmap:mail']
        || sessionData.primaryAccounts?.['urn:ietf:params:jmap:core']
        || Object.keys(sessionData.accounts)[0],
      capabilities: sessionData.capabilities,
      downloadUrl: sessionData.downloadUrl,
      uploadUrl: sessionData.uploadUrl
    };
  
    return this.session;
  }