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

Annotations already declare the safe read-only, non-destructive, non-open-world profile, so the description adds genuine value by disclosing return behavior: each item carries an id usable as the UGC character and thumbnails are attached. This return-format detail is exactly the kind of context annotations don't cover, though it stops short of mentioning ordering, limits, or empty-state behavior.

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, fully front-loaded with the purpose before the output/usage hints, with no redundant or filler content. Every sentence 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?

With no output schema present, the description must carry return-value information, and it does so by noting the id and attached thumbnails. Combined with annotations covering the safety profile, this is nearly complete for a simple list tool, missing only minor details like ordering or result count.

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?

There are zero parameters, so the baseline is 4. The description appropriately spends no words on parameter syntax and instead focuses on outputs, which is the correct choice for a no-arg list tool.

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 (List) and resource (saved characters/actors) with a clear domain qualifier ('for UGC video'), so the agent knows exactly what is being returned. It implicitly distinguishes itself from lookalike siblings like list_character_library and list_seedance_actors via 'your saved characters,' but never names them explicitly, keeping it short of a 5.

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?

Usage is implied rather than stated: 'Each has an id to pass as the UGC character' tells the agent what the output is for, which suggests this is the pre-step before a UGC generation call. However, there is no explicit when-to-use, when-not-to-use, or named alternative versus list_character_library/list_seedance_actors, so it remains at the minimum-viable level.

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