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

The annotations already declare readOnlyHint=true, and the description's 'Lists' phrasing is consistent with that. The description adds modest context by clarifying that the result includes price per image in USD, but does not cover other behavioral aspects like response format or pagination, which is acceptable for a simple read-only listing.

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?

A single sentence that names the action, the resource, and the key returned attribute without any filler. It is efficiently front-loaded and every word adds meaning.

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 zero-parameter, read-only list tool, the description is complete: an agent knows what the tool returns (available models and prices) and why it might call it. No output schema exists, but the simplicity of the operation means no additional context is necessary.

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 tool has zero parameters, so the schema fully covers parameter semantics and there is nothing for the description to compensate for. Baseline 4 is appropriate because the description reinforces what the returned data means rather than parameter syntax.

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 uses the specific verb 'Lists' with a clear resource ('available thumbnail image models') and adds the price-per-image detail, which distinguishes it from siblings like generate_thumbnails and get_generation. An agent can immediately tell this is the catalog tool for model selection.

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 implies this tool is used to see available models and their prices, which is a useful lead-in to generating thumbnails. However, it does not explicitly state when to choose this over sibling tools or mention any exclusion conditions, leaving usage context to inference.

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