Broadcast Flex Message

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

With destructiveHint=true in annotations, the description adds valuable context by specifying the scope of the destructive impact: 'this message will be sent to all users.' This complements rather than contradicts the annotation, giving the agent a concrete sense of the blast radius. No annotation contradiction.

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

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

Three sentences with no wasted words: action+audience, capability (bubble/carousel), and a deliberate warning. The warning in sentence three slightly echoes sentence one's 'all users,' but this repetition is justified emphasis for a destructive broadcast operation.

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

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

For a highly complex, destructive broadcast tool with no output schema, the description covers the core semantics and audience scope but misses operational realities: quota consumption (sibling get_message_quota hints this matters), non-reversibility of broadcasts, and any structural guidance for the message parameter. An agent would benefit from knowing this action cannot be undone.

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

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

Schema description coverage is 0% for the single required 'message' parameter, so the description must compensate. It does add meaningful semantics by explaining the two layout options (bubble and carousel) that map to the contents oneOf in the schema. However, given the extreme complexity of the nested message object, it only scratches the surface—it doesn't mention required altText or the structural rules (e.g., body must be a Box).

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

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

The description states a specific verb (broadcast), resource (flex message), and scope (all users who added the LINE Official Account), making the tool's function unambiguous. It naturally distinguishes itself from siblings like push_flex_message (targeted) and broadcast_text_message (text-only) by naming the audience and message type.

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

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

The description makes the broadcast scope explicit with 'all users who have added your LINE Official Account' and reinforces it with the warning that the message goes to everyone. This clearly implies the push vs broadcast decision context, though it doesn't explicitly name alternatives like push_flex_message or state when not to use it.

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