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

readOnlyHint=true already tells the agent this is a safe read. The description adds real context beyond that: the response covers every shape and color a part can take, flags which ones must be purchased first, and states the currency involved — information that shapes how the agent interprets results. It does not describe pagination or response structure, but nothing suggests those exist.

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?

It is a single dense sentence, but the core subject ('How your character looks') is front-loaded and the enumerated body parts and purchase clauses each carry information. It is slightly run-on but wastes no sentences on 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?

For a one-optional-parameter read tool with no output schema, the description covers what is returned, that purchasable variations are included with their cost, and how the optional parameter changes the target. The only gap is the absent comparison to the sibling that actually changes appearance.

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 coverage is 100%, so the baseline is 3. The description still adds meaning: 'person' must be someone in the room, and supplying it redirects the query from the caller to that target rather than filtering a list. That constraint is not in the schema property text.

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?

The description names a concrete resource — the character's head, ears, hat, torso, arms, bottom and eye colors, plus the shapes and colors available and their purchase requirements. That is far more specific than the title 'Appearance'. It stops short of naming the mutation sibling change_appearance, so the agent must infer that this tool only reads.

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?

It gives one clear usage instruction: pass a person in the room to view their appearance instead of your own. There is no explicit statement about when to use this versus change_appearance, unlock_shape, or inventory, which are the obvious adjacent tools, so routing must be inferred.

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