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

Annotations already establish readOnlyHint=true and destructiveHint=false, so safety is covered. The description adds meaningful behavioral context beyond that: a Skill is guidance to act on and its steps should be applied to the task, which tells the agent how to treat the returned content. It stops short of describing error behavior, such as what happens with a nonexistent slug, which keeps it at 4.

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-loaded with the usage trigger, then the mechanics, then the conceptual distinction from Prompt. Every sentence carries information an agent needs in order to choose correctly.

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 read-only, two-parameter, no-output-schema tool, the definition covers the trigger, the slug prerequisite, the fallback discovery path, and the Skill-versus-Prompt distinction. Nothing required to invoke it correctly is missing.

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 both slug and brand are fully documented in the schema. The description reinforces slug discovery via list_library but says nothing about the brand parameter's default fallback or cross-brand behavior. Baseline 3 is correct given the schema does the heavy lifting.

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 ('Loads a saved Skill by slug') and explicitly contrasts itself with get_prompt and list_library. An agent can distinguish it from every sibling without opening the schema.

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?

Gives the trigger ('when the user asks to use or apply a skill'), a fallback for unknown slugs ('call list_library first'), and an explicit when-not ('do not use it for saved prompts; use get_prompt for those'). This is as complete as guidance gets.

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