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

Goes beyond the annotations by disclosing a side effect the annotations don't cover: an unrecognised tag name silently creates a brand-level tag, not just an association on this creative. It also states the post-call state (returns the creative's tags afterwards) and that the operation is free, which is real cost information. Annotations already cover readOnly=false, idempotent, non-destructive.

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?

Three short sentences, front-loaded with the action and object before the side effect and return value. No filler and nothing repeated from structured fields unnecessarily.

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 a full schema, an output schema, and rich annotations, the description only needs to add the non-obvious bits, which it does (auto-creation and cost). It stops short of covering the 20-item cap or how simultaneous add/remove of the same name resolves, both minor gaps given the schema carries the limits.

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 all four parameters are already documented, including the add/remove semantics and the brandId omission rule. The description's 'by name' phrasing and the auto-create note largely restate the schema's 'Created if they do not exist', adding little beyond the baseline.

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 pair (adding or removing) on a specific resource (a creative in the Library) and the mechanism (by name). An agent can immediately distinguish it from siblings like rename_creative, set_creative_favorite, or edit_creative, which do different things to the same object.

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?

The description makes the operating context clear: tags are addressed by name, and unknown names are created rather than rejected. It does not name an alternative or state when-not to use it, but no sibling overlaps with tag mutation, so the routing risk is low.

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