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

No annotations provided, so description carries full burden. It discloses that currently every plan answers 'This plan is not on sale.' and no order is created, which is crucial behavioral context. However, it doesn't specify what happens on error or success beyond the future return values, nor does it mention authentication needs (the 'email' parameter is unexplained) or rate limits. With output schema present, return format needn't be detailed, but current failure behavior is well-covered.

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?

Two sentences, front-loaded with current unavailability, then future behavior. Efficient and to the point, though the second sentence is somewhat long and could be split for clarity. No wasted words.

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?

Given complexity (3 params, no annotations, output schema exists, 0% schema description coverage), description is somewhat complete: it explains current unavailability and future returns, but misses parameter explanations (especially email) and doesn't guide on alternatives or error handling. Enough to know the tool currently won't work, but not enough to confidently use it when it becomes available or understand parameters.

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 0%, so description must compensate. It mentions 'chosen plan and payment chain' implying plan and chain parameters, but doesn't explain the 'email' parameter at all, nor does it clarify allowed values (enums provided in schema). The description adds minimal meaning beyond what the schema enumerates; it doesn't explain what 'plan' means (standard, pro, alerts) or the significance of 'chain' options.

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+resource ('buy_key') and clarifies current behavior: no keys on sale, every plan returns 'This plan is not on sale.' and no order is created. The future behavior (returns payment address, amount, claim token) clarifies the ultimate purpose, though it's currently non-functional. Distinguished from sibling 'claim_key' by the buying vs claiming distinction, though this isn't explicitly stated.

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?

Implied usage: call this to buy an API key, but currently it always fails. Doesn't explicitly say when to use this vs alternatives like 'claim_key' or 'key_order_status'. The description says 'API keys are not on sale at the moment', which might discourage use, but doesn't provide guidance on what to do instead (e.g., check key_order_status or wait).

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