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

Annotations already declare readOnlyHint=true, destructiveHint=false, and closed-world scope, so safety is covered. The description adds that the response includes signed download and thumbnail links, which is real value, but it does not say whether those links expire, whether 'owned' excludes shared/agency creatives from being returned, or what happens on a miss.

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?

A single front-loaded sentence: the action, the key parameter, and the payload are all in the first clause. Nothing is wasted and nothing is buried.

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?

Fine for a one-param read with annotations covering safety and an output schema covering the return shape. The remaining gap is provenance of selection_key and the semantics of the 'owned' scoping, which an agent needs to call this successfully rather than by trial and error.

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?

One parameter with 0% schema description coverage, so the description has to carry the meaning. It establishes selection_key as the lookup identifier for an owned creative, but never says where the key comes from (creatives_list, creatives_pick?) or its format, leaving the caller to guess.

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?

A specific verb+resource ('Get one owned creative') with the lookup key named and a hint of what comes back (details, signed download and thumbnail links). 'One' and 'owned' separate it from creatives_list and creatives_get_batch, though no sibling is named explicitly.

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: fetch a single creative when you already have a selection_key. There is no statement of when to prefer creatives_get_batch, creatives_pick, or creatives_list instead, and no prerequisite guidance such as needing an id from a prior list/search.

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