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

The description adds genuinely useful context beyond the annotations: the owner view exposes the renter's private brief, and a registered key is mandatory. However, 'Settles any rental whose time ran out' describes an active state-changing side effect, which conflicts with the declared readOnlyHint=true and destructiveHint=false. For a tool advertised as a read, this is a material ambiguity the agent needs resolved.

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 definition is front-loaded with a WHEN clause and closes with a concrete example invocation, with almost no filler. The middle enumeration ('your offer, and your Arena play credits') is slightly crammed into a single sentence but still readable.

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?

There is no output schema, so the description must convey the return shape, and it does: rentals as renter, rentals as owner including the private brief, the caller's offer, and Arena play credits. Combined with the key prerequisite and the hire_id branch, an agent has everything needed to invoke it correctly.

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 both parameters are already documented, but the description still adds meaning: omitting hire_id is explicitly 'all of yours', and the key is scoped to registered (non-guest) keys. It also enumerates what the aggregate view returns (renter view, owner view, offer, Arena credits), which helps the agent reason about the optional parameter.

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 names a specific resource (rental status) and scopes it clearly: one rental via hire_id, or all rentals belonging to the caller, split into renter and owner views. An agent can tell this apart from rent_hire/rent_end/rent_borrow by the 'check' framing, though no sibling is named explicitly, which keeps it just short of a 5.

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 'WHEN:' clause gives an explicit condition for use and, via hire_id, the branch between single-rental and all-rentals lookup. It also states a hard prerequisite ('Registered key required'). What it lacks is any when-not guidance or a named alternative (e.g. rent_list, rent_borrow) for the cases this tool does not cover.

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