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MrNewDelhi

Mailosaur MCP

by MrNewDelhi

mailosaur_messages_create

Create and send email messages to verified external addresses, supporting attachments, CC, and HTML content.

Instructions

Create a message and optionally send it to a verified external address.

Input Schema

TableJSON Schema
NameRequiredDescriptionDefault
serverYesMailosaur server ID.
toYes
ccNo
fromNo
sendNo
subjectNo
textNo
htmlNo
attachmentsNo

Implementation Reference

  • src/index.ts:175-193 (registration)
    Registration of the 'mailosaur_messages_create' tool using server.tool() with name, description, Zod schema for inputs, and handler function.
    server.tool(
      "mailosaur_messages_create",
      "Create a message and optionally send it to a verified external address.",
      {
        server: z.string().describe("Mailosaur server ID."),
        to: z.string(),
        cc: z.string().optional(),
        from: z.string().optional(),
        send: z.boolean().optional(),
        subject: z.string().optional(),
        text: z.string().optional(),
        html: z.string().optional(),
        attachments: z.array(AttachmentSchema).optional()
      },
      async ({ server, ...message }) => {
        const result = await mailosaur.messages.create(server, message);
        return response(result);
      }
    );
  • Input schema for mailosaur_messages_create: server (string), to (string), cc (optional string), from (optional string), send (optional boolean), subject (optional string), text (optional string), html (optional string), attachments (optional array of AttachmentSchema).
    {
      server: z.string().describe("Mailosaur server ID."),
      to: z.string(),
      cc: z.string().optional(),
      from: z.string().optional(),
      send: z.boolean().optional(),
      subject: z.string().optional(),
      text: z.string().optional(),
      html: z.string().optional(),
      attachments: z.array(AttachmentSchema).optional()
    },
  • Handler function that destructures 'server' from args, passes remaining properties to mailosaur.messages.create(), and returns the result via the response() helper.
    async ({ server, ...message }) => {
      const result = await mailosaur.messages.create(server, message);
      return response(result);
    }
  • AttachmentSchema used by the tool's input: id (string), contentType (optional), fileName (optional), content (optional), contentId (optional).
    const AttachmentSchema = z.object({
      id: z.string(),
      contentType: z.string().optional(),
      fileName: z.string().optional(),
      content: z.string().optional(),
      contentId: z.string().optional()
    });
  • The response() helper function used by the handler to format the result as MCP text content.
    function response(value: unknown) {
      return {
        content: [
          {
            type: "text" as const,
            text: JSON.stringify(value, null, 2)
          }
        ]
      };
    }
Behavior2/5

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

With no annotations, the description should disclose behavioral traits. It only mentions 'optionally send' without explaining what happens when sending is disabled (e.g., draft creation) or any side effects, permissions, or rate limits.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness3/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is very concise (one sentence) but lacks structure such as bullet points or sections. For a tool with 9 parameters, this conciseness is insufficient and does not help the agent understand the parameters.

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

Completeness1/5

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

Given 9 parameters, no output schema, and no annotations, the description is severely incomplete. It omits how the tool behaves with optional sends, how to use attachments, and what the response looks like, making it hard for an agent to invoke correctly.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters2/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema description coverage is only 11% (only 'server' has a description). The tool description adds no parameter details, leaving users to infer meanings of 'to', 'send', 'attachments', etc., which are undocumented.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose4/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states the tool creates a message and optionally sends it to a verified external address. However, it does not differentiate from sibling tools like mailosaur_messages_forward or mailosaur_messages_reply, which also involve message creation or modification.

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 usage guidelines are provided. The description does not specify when to use this tool versus alternatives, nor does it mention prerequisites or context for the 'send' option.

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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