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

With no annotations provided, the description must carry behavioral disclosure itself. It reveals that the tool is free and shows a cost breakdown, which is useful. However, it does not explicitly confirm that no side effects occur, whether authentication is needed via npub or dpop_token, or whether it actually executes the target call or merely estimates its cost.

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 compact and front-loaded: the first sentence states the core purpose, and the second provides essential behavioral detail about cost and credits. Every sentence earns its place with no redundancy.

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 output schema exists, so return-value documentation is not the description's job, and tool_id is well explained in the schema. Still, without annotations, the description omits side-effect clarity and leaves npub and dpop_token unexplained, so an agent may lack enough context for a fully correct call.

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 description adds no parameter-level meaning. The schema covers tool_id and tool_kwargs, but npub and dpop_token are undocumented, and overall schema description coverage is only 50%. Since the description does not compensate for these gaps, parameter semantics are weakly supported.

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 uses a specific verb ('Preview') and a clear resource ('the effective cost of a tool call'), then elaborates with what the preview shows: base cost and constraint effects like discounts, free trials, and surge pricing. This distinguishes it from sibling tools like get_pricing_model or check_balance, since the focus is on estimating an individual tool call's 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 implies the tool is used to preview costs before making a tool call, and the 'Free — no credits required' note encourages safe use. However, it does not explicitly say when to prefer this over alternatives, nor does it state when not to use it or what prerequisites apply.

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