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

Annotations already indicate read-only and non-destructive; the description adds that no debit occurs and enumerates the response fields (cost, balance, would_succeed). This is meaningful behavioral context beyond the annotations, though edge cases like rate limits are not mentioned.

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?

One dense sentence delivers the core concept first ('Dry-run cost'), then the endpoint and return fields. No filler or redundant explanation.

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 one-param tool with no output schema, it adequately covers the no-debit behavior and return fields. However, it does not specify the range of acceptable op values, and the title hints at multiple operations, leaving some ambiguity for non-default invocations.

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 schema already fully documents the only parameter (op, default pdf), so the baseline is 3. The description's URL example reinforces the default but doesn't clarify what other operations are valid or how to choose them, adding minimal semantic value.

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: quoting the cost of an operation without debiting, and gives the exact endpoint. The phrase 'without debit' distinguishes it from checkout_credits, making sibling differentiation clear.

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?

Clear context: this is a dry-run cost check, so use it before an operation that might debit credits. It does not explicitly name alternatives or exclusions, but the 'without debit' phrasing implicitly routes away from checkout_credits.

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