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

Annotations mark it non-read-only, non-destructive, non-open-world, but the description adds the crucial behavior the annotations cannot: the async approval flow, that 'applied: true' means an order was placed and funds held (not charged), and that a card decline orders nothing. This is substantial disclosure beyond annotations.

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?

It is a dense but front-loaded paragraph; the core action and the add/phones examples come first, followed by the approval and billing semantics. Every sentence carries load given the complexity, though the density makes it slightly heavy for one block of text.

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?

With no output schema, the description still covers the full lifecycle an agent needs: the required terms acceptance, the approval/denial outcomes, the meaning of 'applied: true', the hold-vs-charge distinction, and the decline path. Nothing essential to correct invocation is missing.

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 coverage is 100%, so the baseline is 3, but the description adds integration semantics that the schema lacks: that 'add: -2' drops two and 'phones: 5' is the target total, clarifying the either/or semantics and the negative-value convention in context of the billing effect.

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 opens with a specific verb+resource and scope: 'Change how many phones the rental covers,' immediately distinguishing it from an initial rental tool like start-rental-tool. Concrete examples ('add: 1', 'add: -2', 'phones: 5') make the exact action unambiguous.

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?

It states the normal flow (files the change, returns a link) and names the exact alternative to poll for the result: 'poll get-billing-request-tool for their answer.' It also spells out the exception path (standing allowance applied straight away) with the condition that selects it, plus the terms precondition.

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