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

Annotations already declare readOnly, idempotent, non-destructive and closed-world. The description adds value beyond that by stating cost/auth posture (free, no sign-in) and by describing what each returned record contains, which the annotations do not cover.

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 tight sentences: the first defines the resource and return shape, the second covers cost/auth and downstream slug usage. No filler, and the identifying information is front-loaded.

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 single-optional-param, read-only lookup with no output schema, the description supplies everything an agent needs: what comes back, that it's free/no-auth, and how to consume the slugs. Nothing material is missing.

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 single `query` parameter is fully documented in the schema (with examples and the 'leave out to list everything' behavior). The description adds nothing about the parameter, so the 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?

States a specific verb (lists/searches) and resource (ad templates, ad features, creation modes) and even describes the per-item return shape (slug, name, one-sentence description). This clearly distinguishes it from the make_*, get_* and list_* siblings.

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 concrete downstream routing: a template slug is passed to ugcfans_make_ad as `template`, a feature slug as `feature`. It also notes the tool is free and needs no sign-in. It lacks explicit when-not-to-use guidance, but no sibling overlaps this lookup role, so the gap is minor.

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