purchase_cost

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

With no annotations, the description carries the full behavioral burden and does it well: it self-declares read-only, describes what a refusal carries (`reason` and `engine_reason`), and warns that Wonders are never purchasable. Adding the engine_reason semantics is genuine context beyond structured fields, though it stops short of pagination/latency/other operational traits.

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?

Front-loads the key fact ("Read-only: cost to rush-buy...") before branching into details. Sentences are dense but each earns its place; the engine_reason sentence is slightly verbose but informative.

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?

No output schema exists, yet the description still explains the returns (cost, can_purchase) and the refusal shape (reason, engine_reason). Combined with the read-only declaration, an agent has enough to call it correctly, though city_id and any error/pagination behavior go unaddressed.

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 0%, so the description must compensate and largely does: it explains the item identifier format (UNIT_.../BUILDING_...) and the yield_type values (GOLD default or FAITH). Only city_id is left undocumented, which is a minor gap given its obviousness.

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: reports the rush-buy cost of an item and whether it is purchasable. It explicitly differentiates itself from the sibling purchase_production by telling the agent to check this first, so the agent can distinguish the two without opening either schema.

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?

Gives an explicit routing rule ("Check this before purchase_production") and a usage caveat (Wonders are never purchasable, so can_purchase reads false). It names the alternative but does not spell out when-not to call it in general terms, keeping it just short of 5.

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