mcp-server-smallinvoice

send_letter_by_post

Send a specified letter by postal mail, choosing color (colour or black&white), printing (duplex or simplex), and speed (priority or economy). Irreversible.

Instructions

Sends specified letter by post (SENDS BY POST — irreversible)

Tool call template

Replace each placeholder with a value matching the input schema. Only required parameters are included; add optional parameters as needed.

{
  "id": 1,
  "jsonrpc": "2.0",
  "method": "tools/call",
  "params": {
    "arguments": {
      "letter_id": "<letter_id>",
      "palette": "<palette>",
      "print": "<print>",
      "speed": "<speed>"
    },
    "name": "send_letter_by_post"
  }
}

Input Schema

Name	Required	Description
`letter_id`	Yes	letter ID
`palette`	Yes	palette; possible values: C - colour, BW - black&white
`print`	Yes	printing type; possible values: D - duplex (two-sided), S - simplex (one-sided)
`speed`	Yes	sending speed; possible values: P - priority, E - economy

Schema Changelog

Changes observed during successful MCP inspections.

First observedv0.1.0May 29, 2026

TDQS

A3.7/5.0

Behavior4/5

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

Description adds the note 'irreversible', which provides behavioral insight beyond annotations (readOnlyHint=false, destructiveHint=false). This warns the action cannot be undone.

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 parenthetical note, no wasted words. Front-loaded with essential information.

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?

For a simple send action, the description is adequate but lacks information about expected outcomes or return format. No output schema, so description could be more complete.

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

Parameters3/5

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

Schema description coverage is 100%, so the schema already documents parameters. Description adds no further parameter information beyond the schema's brief descriptions.

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 sends a letter by post and emphasizes irreversibility. It distinguishes from sibling send_letter_by_email by specifying 'by post'.

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 like send_letter_by_email. Only mentions irreversibility, which is a behavioral note, not usage context.

Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.

Deploy Server