download_skill

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

With no annotations provided, the description must carry the full burden of behavioral disclosure. It clearly states it 'fetches' a payload, implying a read-only operation, and mentions the purchase prerequisite. However, it does not disclose potential errors (e.g., unowned skill), authentication needs (though schema covers the key), or any side effects. For a simple fetch, this is acceptable but not exhaustive.

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 two short sentences with zero fluff. The core action is front-loaded, and the purchase caveat is placed second without unnecessary elaboration. Every word earns its place.

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 tool with only two parameters (one required) and no output schema, the description covers the essential purpose and the key prerequisite. It doesn't mention discovering skills (which might be handled by list_skills or market_listings) but that's not necessary for invoking the tool. Overall, an agent has enough to use it correctly.

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 schema already describes both parameters (id and key) with 100% coverage, including details like 'Skill id (skl_...) or slug' and 'Omit if set as SKILLS123_KEY env'. The description adds no extra semantic meaning beyond what the schema provides, so it hits the baseline of 3 for high coverage.

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 clearly states the verb 'fetch' and the resource 'skill payload (its full instructions/code)', which unambiguously identifies the tool's function. It distinguishes itself from list_skills (which would just list metadata) and purchase_skill (which handles transactions). No ambiguity exists.

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?

The description provides an important usage condition: 'Market skills require purchase first,' which implicitly tells the agent to call purchase_skill before download_skill for market skills. However, it does not explicitly contrast with list_skills or state when to use this over other sibling tools, relying on the agent to infer the purpose from context.

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