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

With no annotations supplied, the description carries the full burden and does disclose two non-schema behaviors: the cost ('Cost: 3 credits') and the return shape ('Returns { generatedImage }'). It omits whether generation is synchronous, whether credits are charged on failure, and any prompt moderation limits — meaningful for a paid generative call.

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 in a logical order: what it does, what it returns and costs, and where to go instead. No filler or redundancy.

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 three-parameter generation tool with no output schema, the description covers purpose, cost, return field, and the primary alternative — enough to call it correctly and predict the charge. Only failure/moderation semantics are absent, which is a minor gap given the schema's completeness.

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 both enums are documented with defaults in the schema, so the description's mention of style and aspect ratio adds no format or constraint detail. Baseline 3 is appropriate when the schema already does the heavy lifting.

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?

States a specific verb and resource ('Generate an image from a text prompt') plus the two optional knobs (style, aspect ratio). It also names the sibling it is not ('For a choice of image models use create_image'), so an agent can distinguish it from create_image without opening either schema.

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?

Gives an explicit routing rule to the alternative create_image when the agent wants model selection, and surfaces the credit cost as a decision input. It stops short of stating when-not to use it at all (e.g., for editing or upscaling an existing image, where siblings like enhance_image or upscale_image apply).

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