appearance_set_color

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

With no annotations, the description carries the full burden and does well: it discloses that an identical copy made earlier is reused (returning "created": false), that library appearances are left untouched, and what the return payload contains. It does not cover permissions or whether the appearance is applied or only created/assigned beyond the implied assignment.

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 the action, then the reuse rule, then the non-mutation caveat, then an explicit return shape and a worked example. Slightly awkward phrasing ('with the RGBA colour is assigned') and the example is near-redundant, but there is no wasted content.

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?

No output schema exists, yet the description spells out the returned keys, the reuse flag, and the scope boundaries (design copies only, library untouched) — enough for correct invocation. What is missing is negligible: no note on how the assignment interacts with occurrence-level overrides.

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 baseline is 3, but the description adds real semantics: `base` falls back to the target's current appearance, and the example shows the `target` ref plus a hex `color`. It does not explain the `name` default beyond the schema, but it does more than restate the schema.

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 (assign a plain colour to a body/face/occurrence) and clarifies the mechanism: it creates a design copy rather than touching library appearances. The scope is clear, though the sibling `appearance_assign` is never named, so the distinction between the two has to be inferred.

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 only implied: 'Library appearances are not changed' and 'a design copy of base' hint that this tool is for creating derived design appearances rather than assigning existing library ones. There is no explicit when-to-use or when-to-prefer-an-alternative statement.

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