@zients/line-mcp-server

Broadcast Flex Message

broadcast_flex_message

Broadcast a rich Flex Message (bubble or carousel) to all LINE Official Account followers using JSON container data and alt text.

Instructions

Broadcast a Flex Message (rich layout) to ALL followers of the LINE Official Account. Use with caution.

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": {
      "altText": "<altText>",
      "contents": "<contents>"
    },
    "name": "broadcast_flex_message"
  }
}

Input Schema

Name	Required	Description	Default
`altText`	Yes	Alternative text shown in push notifications (max 400 chars)
`contents`	Yes	Flex Message container JSON string (bubble or carousel)

Schema Changelog

Changes observed during successful MCP inspections.

First observedv1.0.1Sep 4, 2026

TDQS

A3.6/5.0

Behavior2/5

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

With no annotations, the description must carry the full burden of behavioral disclosure. The only signal is 'Use with caution,' which vaguely hints at potential impact but does not disclose specific behaviors such as message quota consumption, irreversibility, or error handling. An agent cannot assess the full consequences of broadcasting to all followers from this description.

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?

The description is two short sentences with the primary action and target front-loaded. Every word contributes: the action, the resource, the audience, and a caution. No filler or redundant phrasing.

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

Completeness2/5

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

For a broadcast tool with no annotations and no output schema, the description is insufficiently complete. It fails to mention that broadcasting consumes message quota, that the action is irreversible, or that it requires followers to exist. The vague caution does not compensate for the lack of concrete risk and operational details an agent needs to call this tool safely.

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 both parameters (altText and contents) are already documented in the schema. The description adds no parameter-specific details, only the general note that it is a 'rich layout,' which does not go beyond the schema. Baseline of 3 is appropriate.

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 clearly states the action ('Broadcast'), the resource ('a Flex Message (rich layout)'), and the precise target ('ALL followers of the LINE Official Account'). This distinguishes it from push (single user) and multicast (subset) tools. The parenthetical clarifies the message type, 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 scope is explicitly defined as ALL followers, which provides clear context for when to use this tool over push or multicast. However, it does not explicitly name alternatives or provide exclusion conditions, and the cautionary note is generic rather than a direct comparison. Still, the target scope is clear enough to imply usage.

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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