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

With no annotations, the description carries the load and does add useful behavioral context: the operation is free, requires no credits, and reflects constraint effects like discounts and surge pricing. 'Preview' strongly implies it does not execute the underlying tool, though it stops short of explicitly stating that.

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 tool's purpose, then the scope of what it shows, then the free/no-credit footnote. There is no filler or redundant restatement of the tool name.

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?

The presence of an output schema covers return-value expectations, and the free behavior plus preview purpose are clearly communicated. However, the description omits usage timing relative to pricing-model siblings and leaves npub/dpop_token semantics unresolved, so an agent may not be fully equipped to call it correctly in context.

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 covers tool_id and tool_kwargs well, but npub and dpop_token have no descriptions and are not explained in the description. The description does not meaningfully compensate for the 50% schema coverage gap, leaving the optional authentication/context parameters underspecified.

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 states a specific action and resource: 'Preview the effective cost of a tool call,' including base cost and constraint effects. This clearly distinguishes it from most siblings, though it does not explicitly contrast it with related tools like authority_get_pricing_model.

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 naming and phrasing imply this should be used to check the cost of a tool call before executing it, and 'Free — no credits required' signals safe exploratory use. However, there is no explicit when-to-use guidance or comparison to alternatives such as authority_get_pricing_model.

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