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

With no annotations, the description carries the burden and does disclose real behavior: variant_name creates a new look, keeps all animations working, and leaves the current look untouched, which tells the agent the operation is additive rather than destructive. Gaps remain around whether the default in-place edit is reversible, what the call returns (a job id?), and whether it is long-running, which matters given list_jobs/wait_for_job siblings.

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 sentences, tightly packed, with the primary behavior front-loaded and the disambiguation clauses following in order of likely confusion. No filler or restatement of the title.

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 3-parameter mutation tool with no output schema and no annotations, it covers purpose, alternatives, and the variant side effect well. It is slightly incomplete on the return value and whether edits are asynchronous or reversible, which an agent needs before firing the call.

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 0%, so the description must supply semantics, and it does for the two required/optional fields that matter: instruction gets example phrasing and variant_name gets full effect semantics. Only id is left unexplained, though it is inferable as a mascot identifier from the sibling set.

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 ("Change a mascot's design") and immediately characterizes the input as a natural-language instruction with two concrete examples. It is clearly separable from sibling mutators like add_prop and recolor_mascot, which it names and contrasts.

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?

Explicitly routes three alternative intents: separate look via variant_name, worn/held items via add_prop, pure color changes via recolor_mascot. It also states the follow-up mechanism (switch_look), so the agent knows the full workflow, not just this step.

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