purchase_topup

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

With no annotations, the description must convey behavioral traits. It indicates the purchase uses wallet balance (suggestive of a deduction) and requires a valid token, but does not disclose side effects (e.g., wallet balance update, order status change), idempotency, or failure conditions. More detail is needed for a financial transaction.

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 a single concise sentence that gets to the point quickly. It is front-loaded with the action. However, it could be slightly more informative without becoming verbose, such as mentioning the return value.

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 and 3 required parameters, the description is incomplete. It does not explain what happens on success or failure, nor does it mention workflow prerequisites beyond the token. The agent lacks information about the outcome, which is critical for a purchase action.

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 100%, providing descriptions for all three parameters. The tool description adds no additional meaning beyond the schema (e.g., it mentions 'valid session token' but that is already in the schema). Baseline score of 3 is appropriate as the schema already handles parameter understanding.

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 clearly states 'Purchases a compatible top-up package using the wallet balance', providing a specific verb and resource. This distinguishes it from sibling tools like purchase_esim_with_wallet (different type of purchase) and get_topup_packages (listing only).

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 mentions 'Requires a valid session token', indicating a prerequisite, but does not explicitly state when to use this tool versus alternatives like purchase_esim_with_wallet or cancel_order. No exclusions or conditional usage are provided, leaving the agent to infer context.

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