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

With no annotations provided, the description carries the full burden. It explicitly states that the operation is free ('Free — no credits required') and uses 'Preview' and 'Shows' to indicate a read-only, non-mutating behavior. This is valuable context beyond what a schema would provide, though edge cases and side effects are not detailed.

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 three concise sentences with no fluff. The first sentence states the core purpose, the second elaborates on what is shown, and the third adds a key behavioral note about cost. Every sentence earns its place.

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?

Given the tool's simplicity and the presence of an output schema, the description adequately covers the purpose, key behavior, and cost implications. It does not explain return values (not needed due to output schema) but provides enough context for an agent to understand when and how to use it. Missing details about parameter formats are partly covered by the schema.

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 50%; tool_id and tool_kwargs have useful descriptions in the schema, but npub and dpop_token are undocumented. The description adds some context by mentioning constraint effects, which aligns with tool_kwargs usage, but it does not explain the parameters explicitly or compensate for the undocumented ones. Overall it neither enhances nor detracts from the schema.

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 the tool's purpose with a specific verb ('Preview') and resource ('the effective cost of a tool call'). It also lists what the preview includes (base cost, constraint effects like discounts, free trials, surge pricing). This distinguishes it from sibling tools like get_pricing_model, which returns the pricing model configuration rather than a call-specific cost.

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 conveys that this tool is used to preview costs before making a tool call, but it does not explicitly state when to use it versus alternatives. There is no mention of exclusions or alternative tools for similar purposes. The context is clear enough for basic use but lacks explicit guidance.

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