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

Annotations already mark readOnly/openWorld/idempotent, but the description adds genuinely useful behavior: prices are read live from the door manifest rather than a stale table, the door's own 402 challenge is the final price truth, and each call is paid from the caller's own wallet at call time. This goes well beyond the structured hints.

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 sentences, all substantive, with the main purpose front-loaded. It is slightly longer than strictly necessary—'Free, keyless, read-only' partially repeats annotations—but every sentence earns its place by clarifying cost semantics, freshness, or workflow.

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 output schema exists, one optional parameter, and read-only annotations, the description is complete enough for an agent to decide when to call it and what to expect: full price list, sorted cheapest first, live source, no wallet balance interaction, and final authority delegated to the door's 402 response.

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 100%, so the single optional maxUsd parameter is already documented. The description adds useful context like 'cheapest first' but does not discuss the ceiling filter; the schema carries that weight, so the baseline of 3 is appropriate.

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 identifies the resource: 'the whole price list for this server's paid doors, in dollars, cheapest first.' It is phrased as a noun phrase rather than an explicit imperative verb, and it does not call out a sibling by name, but the function is unmistakable and the 'budget BEFORE committing' framing distinguishes it from payment execution tools.

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?

Explicitly instructs when to use it: 'Use it to budget BEFORE committing to a call.' It also names the alternative behavior—without it, the only way to learn a price is to call a door and read the 402—and clarifies that there is no balance to top up, so agents know not to treat this as a wallet or prepayment tool.

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