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

Annotations already declare the safe read profile (readOnlyHint, idempotentHint, non-destructive, non-open-world), so the bar is lower. The description adds genuinely new behavior: no authentication required, and results differ by auth state (signed out = full price list, signed in = entitlement-filtered offer). It does not mention pagination or caching, so not a 5.

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 purpose is front-loaded in the opening clause and every sentence carries information (payload, cost unit, auth behavior, downstream consumers). The final sentence runs long and packs several ideas together, costing some scannability.

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, the description must describe return content, and it does: qualities, per-unit credit costs, plan gating, and the accepted model ids. Combined with the auth-state explanation, an agent has enough to call and use it, though exact field shapes and ordering remain unspecified.

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% with a single optional enum ('kind'), so the schema already carries the parameter meaning; baseline 3 applies. The description adds adjacent context (plan locks, per-account availability) but never explains the kind filter or the enum values.

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 ('Lists what UGC Fans makes at each quality') plus the payload (stills, clips, talking clips, credit cost per unit, plan locks, model ids). This clearly separates it from siblings like ugcfans_estimate (pricing computation) and the make_* tools (which consume the ids listed here).

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 clear context: it is free and needs no sign-in, and it explains that the returned model ids are the ones ugcfans_estimate and the make tools accept, which implicitly routes the agent to call this first. It stops short of explicit when-not-to-use or a named alternative for overlapping lookups.

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