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

Annotations already declare destructiveHint=true and idempotentHint=false, but the description adds real behavior beyond them: the purchase consumes Luck Points and automatically equips the item. It still omits failure modes (insufficient Luck Points) and what happens to any currently equipped cosmetic.

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?

A single front-loaded sentence that names the action, the cost, and the side effect with zero filler.

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 one-parameter mutation with full annotation coverage and no output schema, the description covers the essentials (cost and auto-equip). Only edge-case behavior (insufficient funds, re-equip semantics) 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% and the single itemId parameter is documented as coming from list_cosmetics, so the schema carries the load. The description adds nothing about itemId syntax or format, making the baseline 3 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?

States a specific verb and resource ('Buys a cosmetic item'), plus the currency (Luck Points) and a key side effect ('equips it'). This distinguishes it reasonably from the sibling equip_cosmetic, though it doesn't explicitly say how it relates to already-owned items.

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?

No when-to-use or when-not-to-use guidance, no mention of prerequisites such as having enough Luck Points, and no explicit routing to alternatives like equip_cosmetic. The only implicit hint is the schema note 'From list_cosmetics'.

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