Design LINE Imagemap (Rich Message)

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

Annotations indicate readOnlyHint=true, idempotentHint=true, destructiveHint=false, which align with the description's claim of being design-only and not calling the LINE API. The description adds essential details like no upload API, forced canvas width, and return format, going beyond annotations.

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 front-loaded with the core purpose, followed by critical usage details and an example. Every sentence adds value, and the structure is logical and easy to parse.

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 the complexity (nested objects, 5 parameters, no output schema), the description covers the workflow, constraints, and return format. The output structure is briefly mentioned as '{ message, usage_hint }', but could be more detailed. However, it is largely sufficient for the agent to select and invoke 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?

Schema description coverage is 100%, and the description adds value by explaining the image size suffix mechanism for base_url, the coordinate system for bounds, and the absence of an upload API. The example further clarifies parameter usage.

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 starts with 'Build a validated Imagemap message' and explicitly states 'DESIGN ONLY — never calls the LINE API', clearly distinguishing it from siblings like line_send_message and other design tools. The verb and resource are specific and unambiguous.

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?

Provides explicit guidance on when to use (design only), how to use (hand output to line_send_message via message.message_json), and critical prerequisites (pre-host images, coordinate system). The image hosting caveat and canvas width constraint are clearly stated.

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