Add traffic to a residential proxy

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

Annotations already flag destructiveHint=true, idempotentHint=false and openWorldHint=true, so the safety profile is covered. The description adds genuinely new behavioral context: the account balance is charged immediately, geo settings and the connection string are preserved, and estimate_only suppresses the charge. It does not mention failure modes such as insufficient balance or a bad price_id.

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?

Three compact sentences, each carrying distinct information (what it does, billing behavior, where to verify the result), with the core action front-loaded and no filler.

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 mutating tool with no output schema, the description covers the key concerns: immediate billing, settings preservation, the estimate-only escape hatch, and how to observe the resulting quota. It stops short of stating prerequisites (valid price_id, sufficient balance) or error behavior, which an agent might need before committing money.

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 100%, so all four parameters are already documented, including estimate_only and the num multiplier semantics. The description only reinforces estimate_only and points to where the resulting quota is visible (residential_traffic_left_mb in list_proxies), which is useful but not parameter-level detail beyond the schema. Baseline 3 applies.

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 ('tops up') and resource ('traffic quota of an existing residential proxy'), and the word 'existing' implicitly distinguishes it from buy_residential/buy_proxy which create new proxies. An agent can tell what this does without opening the 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?

The description gives a clear decision rule for the main fork: charge immediately by default, or set estimate_only=true to price without charging. It does not explicitly name the alternative tool for acquiring a new proxy (buy_residential), so the 'when not to use' case is left to inference.

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