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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds value beyond that by disclosing output shape and 'Cost: free, no key', which tells the agent no auth or payment is required to call it. It stops short of describing response size or ordering.

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?

Four short fragments: trigger, inputs, output, cost. Every sentence carries information, and the trigger leads. Nothing is padded or repeated.

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 no-parameter, no-output-schema lookup tool, the description fully equips an agent: it knows when to call, that no arguments are needed, what the JSON contains, and that the call is free with no key.

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?

Zero parameters, so the baseline is 4; the description correctly and explicitly reinforces this with 'Inputs: none', removing any doubt that the call is argument-free.

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 retrievable resource (pricing / how to buy) and enumerates the payload: free key, monthly plans with Stripe links, prepaid credit packs, and per-tool cost. Siblings (html_to_pdf, preview_pdf, render_template) are unrelated enough that no explicit differentiation is needed, though list_capabilities is adjacent and is not contrasted.

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?

'Use when the user asks about price, hits a quota, or needs more documents' gives three concrete invocation triggers, including a non-obvious one (quota exhaustion). No when-not guidance or explicit alternative is named, which keeps it short of a 5.

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