Courier

send_message_to_list

Send a message to all subscribers of a list using inline title and body content. API reference: https://www.courier.com/docs/api-reference/send/send-a-message.

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": {
      "list_id": "<list_id>",
      "title": "<title>",
      "body": "<body>"
    },
    "name": "send_message_to_list"
  }
}

Input Schema

Name	Required	Description	Default
`body`	Yes	Message body
`data`	No	Key-value data to include
`title`	Yes	Message title
`method`	No	Routing method	all
`list_id`	Yes	The list ID to send to
`channels`	No	Channel names to route through. Omit to use default routing.

Schema Changelog

Changes observed during successful MCP inspections.

First observedApr 14, 2026

TDQS

A3.9/5.0

Behavior3/5

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

Annotations already carry the readOnly/idempotent/destructive flags, and the description is consistent with them, so there is no contradiction. The description adds that this targets all list subscribers and uses inline content, but it does not disclose return shape or other side-effect details beyond what 'Send' implies.

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?

A single direct sentence states the core purpose and content mode, followed by a useful API reference URL. There is no filler or repeated title.

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?

Given no output schema and six parameters, the description is adequate but not rich: it identifies the target and content mode, while the schema covers field details. It leaves unaddressed the difference from template-based sends and does not describe the response, though the API reference mitigates this.

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?

With 100% schema description coverage, the schema already documents all 6 parameters, including the method enum, data, and channels. The description adds no parameter semantics beyond mapping 'title' and 'body' to inline content, so the baseline of 3 applies.

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?

The description uses a specific verb ('Send') plus a resource ('message to all subscribers of a list'), and clarifies it uses inline title and body rather than a template. This distinguishes it from siblings like send_message_to_list_template and send_message, making the purpose unambiguous.

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?

The phrase 'to all subscribers of a list' and 'using inline title and body content' gives a clear context for choosing this tool over template-based or single-recipient senders. It does not explicitly name a sibling or provide when-not-to-use guidance, but the intended use case is evident.

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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