purchase_skill

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

No annotations are provided, so the description must carry the behavioral burden. It discloses the revenue split (80% seller, 20% platform) and that credits are consumed, which is useful. However, it does not mention whether the purchase is irreversible, what happens on insufficient credits, or any authentication requirements beyond the optional key parameter. The pointer to download_skill implies a follow-up step but does not fully explain the state change or potential errors.

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 sentences, front-loading the core action ('Buy a market skill') and then providing the cost split and the next step. Every sentence adds distinct value with no unnecessary fluff, making it highly 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?

The tool is simple with only two parameters and no output schema, but the description omits the return value or confirmation behavior. It does hint at the need to use download_skill afterward, which is helpful. However, an agent might need to know what a successful purchase returns (e.g., an ID or immediate access), and that information is missing. Given the simplicity, a 3 is fair.

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 covers both parameters with descriptions (100% coverage), so the description does not need to add much. It does not elaborate on listing_id format or key omission, but the schema covers these. The description adds no new parameter-specific meaning, so the baseline of 3 is appropriate.

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 ('Buy') and a clear resource ('market skill'), and clarifies the payment method ('with your credits'). It also explicitly names the follow-up tool (download_skill), which helps distinguish it from siblings like market_listings and publish_skill.

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 clearly indicates that this tool is for purchasing skills and implies it should be used after browsing listings (market_listings) and before download_skill. It does not explicitly list exclusion criteria or compare to alternatives, but the usage context is clear enough for an agent to select it appropriately.

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