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

With no annotations, the description carries the full burden and does well: it discloses that the call is synchronous ('Waits for results'), the return form (image URLs valid for one hour), the billing model (per image, charged to the API key's account), and a volume cap. It does not cover failure modes, rate limits, or whether expired URLs can be refreshed.

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, front-loaded with the action, then behavior, then cost. Every sentence carries information an agent needs and there is no filler or repetition of the title.

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 four-parameter generation tool with no output schema and no annotations, the description covers the essentials: synchronous behavior, return value lifetime, and billing. The main omission is error/timeout behavior, and the stated 'up to 8 images per call' is not reconciled with the schema limits (n max 4, models max 4).

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 already explains n, format, models, and prompt in detail. The description adds only that multiple models may be combined and that output is billed per image; it adds no new meaning for the individual parameters, so the baseline of 3 applies.

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 a specific verb and resource: 'Generates thumbnail images from a prompt with one or more models.' This distinguishes it from get_generation, list_models, and account_usage in practice, but it never names those siblings or states the boundary explicitly, so sibling differentiation is inferred rather than stated.

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?

Usage is only implied: 'from a prompt with one or more models' tells the agent what input is needed, and the schema notes that model ids come from list_models. There is no explicit when-to-use versus when-not guidance, no prerequisites, and no mention of what to do if a call fails or times out.

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