Simpler.Asia

invoice_message_prepare

Read-only

Prepare what a business sends a client about one issued invoice: purpose 'invoice', 'reminder' (overdue), 'receipt' (paid in full) or 'promise_follow_up' (promised date passed); left out, the one that fits. language 'en', 'ms' or 'zh'; left out, the client's (invoice_client_update message_language), else English. Returns to, subject, body, share_text, a mailto and link_on; share_url only for a member or above with a live link (never made here). NOTHING IS SENT. Refusals (CONFLICT): draft SIMPLER_SALES_MESSAGE_NOT_ISSUED (issue it with invoice_update status 'sent'); cancelled; written off; SIMPLER_SALES_MESSAGE_PURPOSE_UNFIT (send its next_call). Other arguments: VALIDATION_ERROR. Free.

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": {
      "id": "<id>"
    },
    "name": "invoice_message_prepare"
  }
}

Input Schema

Name	Required	Description
`id`	Yes	The invoice's id, from invoice_list or invoice_read.
`purpose`	No	'invoice' sends the invoice, 'reminder' asks for payment, 'receipt' thanks the client once it is paid in full, 'promise_follow_up' asks when to expect a payment the client promised by a date that has passed (invoice_promise_set). Leave out to get the one that fits the invoice's state.
`language`	No	'en' English, 'ms' Bahasa Melayu, 'zh' Chinese. Leave out to use the client's message_language (English when none is set).

Schema Changelog

Changes observed during successful MCP inspections.

First observedOct 23, 2026

TDQS

A4.6/5.0

Behavior5/5

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

Adds substantial context beyond readOnlyHint: 'NOTHING IS SENT' confirms the read-only nature in plain terms, errors are enumerated with codes and remedies (SIMPLER_SALES_MESSAGE_NOT_ISSUED, cancelled, written off, SIMPLER_SALES_MESSAGE_PURPOSE_UNFIT, VALIDATION_ERROR), share_url is permission-gated and 'never made here', and the tool is declared 'Free'. This is exactly the behavioral load annotations alone cannot carry.

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

Conciseness4/5

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

Front-loaded with the core action and purposes, then returns, then refusal paths — logical order with zero filler. The semicolon-chained telegraphic style is dense enough to slow parsing slightly, but nothing is redundant.

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?

No output schema exists, yet the description names the returned fields (to, subject, body, share_text, mailto, link_on, conditional share_url), so an agent knows what it will get. Combined with the refusal taxonomy and the no-send guarantee, nothing needed to call this correctly is missing.

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?

Schema coverage is already 100%, so baseline is 3; the description goes further by explaining how the default purpose is chosen ('the one that fits') and where the default language comes from (the client's message_language via invoice_client_update, else English). Only the 'id' parameter is left entirely to the schema.

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?

Opens with a specific verb+resource ('Prepare what a business sends a client about one issued invoice') and enumerates the four purposes with the condition each corresponds to. An agent can tell this is a non-sending draft generator, distinct from invoice_share or invoice_pdf, without opening the schema.

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

Usage Guidelines4/5

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

Clearly states when each purpose applies ('reminder' for overdue, 'receipt' for paid in full, 'promise_follow_up' after a passed promised date) and gives the remediation path for refusals ('issue it with invoice_update status 'sent'', 'send its next_call'). It does not explicitly contrast with siblings like invoice_share or invoice_reminders_due, so 4 rather than 5.

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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