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

Adds substantial behavior beyond annotations: synchronous completion ("Finishes within the call"), billing semantics ("credits are charged only when a portrait comes back"), automated defect checking on hands/face/background, and the full auth path with header format. These are exactly the cost, latency and auth facts an agent needs before invoking a credit-consuming generation.

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-loads what the tool produces and its consumer before prerequisites and auth. The auth sentence is long and includes a URL and header example, but every clause is actionable; no filler.

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 an output schema present, return values need no explanation, and the description covers the remaining gaps: prerequisite quote, cost timing, synchronous behavior, quality checking and authentication. An agent has everything needed to call this correctly on the first try.

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 prompt, save_as, quote_id and aspect_ratio (with enum) are already fully documented. The description only restates the quote_id provenance that the schema already carries, adding no format or behavioral detail beyond it. 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 and resource ("Generate a creator portrait") plus its downstream consumer (avatar in generate_ad) and the quality check applied. This clearly separates it from generate_image and generate_video in the sibling list.

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 explicit prerequisites: a quote_id from estimate_ad_cost with kind "avatar", and sign-in via OAuth or API key. It doesn't explicitly state when to prefer generate_image instead, but the fixed workflow chain (estimate_ad_cost → generate_avatar → generate_ad) makes usage unambiguous.

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