List models and prices

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

Annotations already mark it readOnlyHint, idempotentHint, and destructiveHint false. The description adds that it is 'free', which is not in the annotations, and that it returns model ids and credit costs. This is useful behavioral context beyond the structured fields and does not contradict them.

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 two sentences, front-loaded with the core return value, then usage guidance. Every clause earns its place with no fluff.

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 low-complexity tool with one optional parameter and no output schema, the description covers what it returns, when to use it, and its cost. A minor gap is that it doesn't explicitly state that omitting the category returns all models, but that is inferable from the schema's 'optional filter' phrasing.

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 single optional 'category' parameter is fully documented in the schema with an enum and description. The tool description loosely aligns with the enum values by listing 'images, video, audio', but it adds no new semantic detail beyond what the schema already provides, so the baseline 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 states a specific verb and resource: 'Returns available models and their cost in credits'. It names the categories (images, video, audio) and explicitly positions itself as the pre-generation lookup tool, distinguishing it from generation siblings like fattly_generate_image and from fattly_credits which likely reports account balance.

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 clear usage context: 'Use before generating to pick the right model id and to tell the user what a generation will cost.' This tells when to call it, though it does not explicitly name alternatives or state when not to use it, stopping just short of a full 5.

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