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

With no annotations, the description carries the full burden and does disclose the key traits: it is a preview/suggestion step rather than a creation step, and it 'costs nothing' (no credits consumed). What it does not state explicitly is that no character records are persisted and that output is a set of looks the user may later approve — both are strongly implied but not spelled out.

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?

Front-loaded with the purpose, then the trigger, then the cost note and follow-on options — a sensible order with no filler. It runs slightly long with the trailing clause about the film designing its own cast, but that clause earns its place by preventing a wrong sequencing choice.

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 an 8-parameter, zero-annotation, no-output-schema tool, the description covers purpose, sequencing, cost, and follow-on paths, which is close to what an agent needs. The remaining gap is return shape — it never says the caller receives a list of named characters with looks — though 'each with a fitting look' hints at it.

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 all eight parameters are already documented, including the preset enum default and the own-story field set. The description's only added meaning is the library-versus-own-story framing, which the schema mostly covers on its own. 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?

Opens with a concrete framing ('Who is in a 3D film') and names the exact resource produced: main characters of a library or own story, each with a look for the chosen preset. It also distinguishes itself from the related siblings by naming create_3d_character and create_3d_film, so the agent can place it in the workflow without opening a 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 trigger ('when the user wants to see or approve the characters, or asks who is in the story') plus the sequencing rule ('Call it before create_3d_character'). It also covers the alternative path of skipping straight to create_3d_film and letting the film design its own cast, which is exactly the when-not guidance an agent needs.

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