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

Annotations only declare readOnlyHint=false; the description adds real behavioral context: the payment currency (copper) and the outcome that the purchased perk is placed into the perk panel, making the mutation's side effect predictable. It does not cover failure behavior, but it goes meaningfully beyond the annotation.

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?

One front-loaded sentence with the action first and clarifying parentheticals after; nothing is redundant. The nested clauses make it slightly denser than necessary but every clause adds information.

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 purchase mutation with no output schema, it covers cost, required shop state, resulting state, and the follow-up tool for applying the perk. Only failure conditions and the ID source are 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?

With 0% schema description coverage, the description must carry the parameter meaning, and it only implies that the single parameter identifies the perk taken from the open shop window. It does not say how to obtain the item_id or what its format is, leaving a real gap for a 0%-covered parameter.

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 opens with a specific verb and resource ('Купить ... один перк') and adds scope (for copper, from the open game_perk_shop window). It also names the sibling that handles a nearby-but-different operation (game_use_item), so an agent can distinguish them 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?

It states a clear precondition — the shop window must already be open — and routes perk application to game_use_item rather than this tool. It stops short of explicit when-not-to-use cases such as insufficient copper or buying outside a shop session.

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