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

Annotations already declare this as read-only, idempotent, non-destructive, and non-open-world. The description adds useful behavioral context by describing the returned character identifiers and URLs and how they are consumed by sibling tools. It does not describe pagination behavior, but the single `limit` parameter is documented in the schema.

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 front-loaded with the listing purpose, then efficiently covers returned fields and downstream usage. The final sentence fragment about the portrait/thumbnail URL is useful but slightly less tightly structured than the rest.

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 simple read-only list tool with no output schema, the description sufficiently explains what is returned (`character_id`, `character_sheet_url`, portrait/thumbnail URL) and how those values are used. Annotations cover the safety profile, and the schema covers the sole parameter.

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%, and the only parameter (`limit`) is fully documented there with a default and maximum. The description does not add parameter-level semantics, so baseline 3 is appropriate.

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 uses a specific verb and resource: "List the authenticated user's saved, reusable characters." It also explains the returned identifier formats (`character_id`, `character_sheet_url`) and distinguishes this listing tool from generation siblings by naming where its outputs are consumed.

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?

It clearly states the downstream usage: pass a character_id or sheet URL as `make_ugc`'s `character`, or use the sheet/portrait URL in `refs` for advanced `generate_video` / `generate_image`. It does not explicitly say when not to use this tool versus alternatives like `get_uploads`, but the intended context is clear.

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