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

Annotations already declare non-readonly, non-idempotent, non-destructive, open-world behavior. The description adds that this is a real charge against a stored card and that omission selects the default card, but omits currency, failure behavior, and the practical consequence of retrying a non-idempotent charge.

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 short sentences, front-loaded with the action and followed by the one non-obvious parameter rule. No filler or repetition of the title.

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?

A financial mutation with no output schema needs more disclosure about the charge result, failure modes, and retry semantics; the description is adequate for choosing the tool but thin for invoking it safely.

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 carry meaning and does explain the optional payment_method_id: omitting it charges the default saved card. The amount parameter is only implicitly explained as 'the amount added to this wallet', with no currency or formatting guidance, so it is not fully compensated.

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: charges a saved card and credits this wallet. The title and description together make it clearly distinct from siblings like list_payment_methods or refund_wallet_topup.

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 implies when to use it (topping up with an already-saved card) and explains the default-card fallback, but never states when not to use it or points to alternatives such as buying a number or setting auto top-up.

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