Design LINE Card Message (Template)

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false. The description adds further transparency by stating 'DESIGN ONLY — never calls the LINE API' and describing the validation and return format. There is no contradiction with annotations, and the description provides useful behavioral context beyond the safety hints.

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?

The description is well-structured with bullet points and an example, making it easy to parse. It front-loads the key message about design-only and JSON return. While it is somewhat long, the content is valuable and organized. Minor improvement: could be slightly more concise, but overall efficient.

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?

Given 7 parameters (2 required) and no output schema, the description covers the important aspects: return format ({ message, usage_hint }), key constraints per kind, and an example. The only gap is the lack of detail on the 'usage_hint' field, but overall it provides sufficient context for an AI agent to use the tool correctly.

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?

The input schema covers 100% of parameters, but the description adds significant value by explaining the different kinds (buttons, confirm, etc.) and their specific constraints (e.g., text length limits, action count rules). It also clarifies the required fields per kind and the expected structure of actions. This goes beyond mere schema listings.

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 clearly states the tool's purpose: to build a validated LINE Template message (card message) and return JSON for use with line_send_message. It emphasizes it is design-only and never calls the LINE API, distinguishing it from sibling tools like line_send_message that actually send messages.

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 explains when to use this tool: to design a card message before sending it via line_send_message. It provides explicit constraints per kind (e.g., buttons, confirm) and notes that the tool is design-only. While it contrasts with line_send_message, it does not explicitly mention other alternative methods (e.g., manual JSON construction), but the guidance is still clear.

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