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

Annotations only provide readOnlyHint=false, destructiveHint=false, etc., which offer little. The description adds behavioral context by stating that the skill 'Merges into the workspace Skills library', implying a persistent, non-destructive addition. It also instructs to 'Distill an imperative, self-contained directive', providing guidance on the content. However, it does not disclose details like overwrite behavior or reversibility, which would be useful for a mutation tool.

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?

The description is three sentences and front-loads the core definition of a skill. It is informative without being excessively verbose. Each sentence adds value: definition, guidance on creating the directive, and the destination (library). Could be slightly more concise, but current structure is efficient.

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 simple tool with two parameters and no output schema, the description is complete enough for an agent to call it correctly. It explains what to save, how to write the directive, and where it ends up. It lacks details on error handling or overwrite semantics, but these are not critical for a straightforward save operation given the annotations.

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?

The input schema already documents both parameters (name and directive) with descriptions, achieving 100% coverage. The description adds meaning beyond the schema by explaining what a skill is (creative directive/playbook) and providing examples, which helps the agent formulate the directive appropriately. This elevates it above the baseline of 3.

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 uses a specific verb ('Save') and resource ('reusable custom SKILL') and clearly distinguishes it from related tools like list_skills and delete_skill. It explains what a skill is (creative directive/playbook) with concrete examples, so an agent can understand exactly what to store without ambiguity.

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 provides clear context for when to use this tool: when saving a new custom skill. It mentions that list_skills displays built-ins plus custom skills, indirectly indicating where the saved item will appear. However, it does not explicitly state alternatives or exclusions (e.g., 'use get_skill to retrieve, delete_skill to remove'), but the purpose is self-evident and no direct sibling competes for the same action.

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