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

No annotations are provided, so the description carries the burden, and 'Reads only' is a valuable safety disclosure plus the 'library and drafts' note tells the agent results include unpublished items. Beyond that it is silent on ordering, volume, or what a 'picture' actually resolves to.

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 with zero filler, the resource scope stated first and the call triggers immediately after. Every clause earns its place.

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 tool with no output schema and no annotations, the description covers what it returns (characters plus pictures), when to call it, and that it is non-mutating. Only the absence of any hint about result shape or volume keeps it below the top mark.

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 takes zero parameters, so there is no parameter semantics to explain and the baseline of 4 applies. The description correctly adds no parameter-shaped detail, which is the right call.

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 — the user's 3D film characters, drawing from both library and drafts, including their pictures. That scope clause meaningfully separates it from list_characters and list_3d_shots, though it never names those siblings outright, so the agent must infer the 3D-vs-2D split.

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 three concrete call triggers: before casting a film, when the user asks who they have, and when looking up a name. This is real when-to-use guidance rather than implied usage. It stops short of an explicit exclusion or naming the alternative list tool for 2D characters.

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