Buy tokens for this key

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

The description adds meaningful behavior beyond the annotations: tokens arrive asynchronously, the payment may be automatically charged or require human checkout, and the key's spend cap cannot be raised by a purchase. It also documents the two main response outcomes (`charged` and `requires_human`) without an output schema.

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?

The description is three sentences with no filler. It leads with the primary action, follows with restrictions, and then explains response behavior and the subsequent polling step.

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 no output schema, the description adequately supplies response semantics, asynchronous delivery, and the follow-up polling instruction. Together with the schema's package guidance, an agent has enough context to call this tool correctly.

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?

The input schema already fully documents the single `package` parameter, including its source (`list_token_packages`) and an example value (`"600"`). The description does not need to add parameter-level detail, so the baseline of 3 is 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?

The opening phrase "Buy one token package for this key's wallet" names a specific action, resource, and target object. It is immediately distinguishable from sibling tools like list_token_packages and get_balance.

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?

The description gives explicit preconditions: the key must have purchasing enabled and the purchase cannot exceed the key's remaining spend cap. It also tells the agent to poll get_balance afterward, clarifying what happens after this tool completes.

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