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

Annotations already declare readOnlyHint=true, idempotentHint=true and destructiveHint=false, so safety is covered. The description still adds real value beyond them by stating the auth requirement ('Requires OAuth or an API key') and reaffirming 'Charges nothing', which is the domain-critical trait for a cost-estimation call. It does not cover rate limits or caching behavior, keeping it below a 5.

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 sentences, front-loaded with the return payload, then the imperative guidance, then the cost/auth footnotes. Dense but every clause carries information; only the long enumeration in the first sentence slightly dilutes readability.

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?

With no output schema, the description carries the burden of describing return values and does so thoroughly (credits, prior charges, balance, model, effort). Auth and cost behavior are stated; only the lone input parameter goes unexplained, a minor gap for a single obvious integer id.

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 the description would ideally clarify the single parameter, but it never mentions project_id or its format. The lone param is self-evident by name, and the description does clarify a related concept (the type='hierarchy' flag on the sibling call), which is useful but not about this tool's own input.

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 names a specific verb and resource ('Returns the credits the analysis ... will cost') and enumerates exactly what comes back: cost, whether credits were already charged, available balance, model and effort. That is clearly distinguishable from siblings like open_end_get_pricing (generic pricing) and open_end_start_run (execution).

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?

It gives an explicit imperative with ordering: 'Always call it and show the user the price and model before open_end_start_run with type='hierarchy''. The condition that selects the follow-up tool and the required user-facing step are both spelled out, leaving nothing to inference.

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