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

Annotations already declare readOnlyHint=true, so the agent knows this is a safe read; the description's added value is that results are restricted to models the calling user can actually generate with and are organized by kind. It says nothing about result volume, ordering, pagination, or what happens when the filter is omitted. With the safety profile already covered by annotations, a 3 is appropriate.

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?

Two short sentences, no filler, with the resource statement front-loaded and the sibling disambiguation second. The first sentence is an elliptical fragment that reads slightly awkwardly, which keeps it just short of a 5.

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-required-parameter, read-only listing tool with an output schema (so return shape needn't be explained), the definition covers purpose and sibling routing adequately. The remaining gap is that an agent cannot tell from the description whether calling with no modality returns all models or errors — a small but real omission.

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 coverage is 100% and the modality parameter already documents its allowed values, so the description's parenthetical list of kinds merely repeats the schema. It does not say that modality is optional or that omitting it returns every kind — the one piece of parameter behavior the schema leaves implicit. Baseline 3 for a fully documented single-parameter schema.

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 identifies the resource (the set of generation models) and its scoping (models the user can generate with) plus the filter dimension (image, video, audio, text), and it explicitly contrasts with the sibling get_model, which returns a single model's inputs and settings. The only weakness is that it is written as a noun phrase with no verb, so the listing action is implied 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?

The second sentence routes the agent: use this tool to survey available models, use get_model when you need one model's inputs and settings. That is a real when-to-use/when-to-use-the-alternative rule. It stops short of explicit exclusions (e.g., that this tool does not return pricing or per-model settings), so a 4 rather than a 5.

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