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

Annotations already declare destructiveHint=true, readOnlyHint=false, and non-idempotent, so the safety profile is covered. The description adds the payment-mode distinction, which is useful, but it does not disclose the irreversibility of spending, balance requirements, or what a failed purchase does.

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 with no filler that puts the primary action and the payment alternative in one breath. Efficient, though the parenthetical could be integrated more cleanly.

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 mutation tool with no output schema, the description plus annotations reasonably cover the core behavior and the primary branching dimension (payment mode). Missing details are return/failure behavior and the effect of qty, but the essentials for calling it correctly are present.

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 coverage is 60%, and the description adds real meaning to pay_with by explaining the "points" value for house goods that the bare enum does not convey. However, qty, input, and item_id receive no clarification in the description, so it only partially compensates for the coverage gap.

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 names a specific verb (buy) and resource (market item) and clarifies the two payment modes (credits vs. reward points on house goods). This is clear, though it does not explicitly distinguish itself from nearby purchase siblings like buy_house_plan or buy_rate_boost.

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 gives one usage cue: use pay_with="points" for house goods. There is no guidance on when not to use it, prerequisites (e.g., sufficient balance), or what alternatives exist, so usage is only implied.

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