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

Annotations already provide readOnlyHint=true, and the description adds complementary behavioral context: it is FREE, prompt-only, does not generate images itself, and returns a downstream-ready prompt. There is no contradiction, and the added cost and side-effect note goes beyond what annotations state.

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 short sentences, each earning its place: free/cost signal, core behavior, and routing to the preferred alternative. Key information is front-loaded and there is no filler or repetition.

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 planning tool with 100% schema coverage and readOnlyHint, the description sufficiently describes what is returned ('the plan and the exact prompt') and how to consume it elsewhere. It could say a bit more about the shape of the plan, but the description is adequate for an agent to select and call it 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%, so the schema fully documents the 10 parameters. The description adds only a high-level statement that plan_sheet 'takes what generate_sheet takes' and mentions output parameters like prompt and aspect_ratio, but it does not need to compensate for schema gaps because the schema already carries that burden.

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 and resource: it 'returns the plan and the exact prompt' for sheets, and positions itself as the 'prompt-only door'. It explicitly contrasts with generate_sheet and generate_image, so an agent can distinguish it from the closest siblings.

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 gives explicit usage direction: use plan_sheet only to generate elsewhere with generate_image, and 'prefer generate_sheet' for the normal path because it 'keeps the prompt server-side and quotes with dry_run'. This directly answers when to use this tool versus the alternative.

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