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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so safety is covered. The description adds two things the annotations cannot: a deterministic newest-first ordering and the required auth scope ("Needs billing:checkout"), which is exactly the kind of pre-call context an agent needs. It does not say what an empty result or a missing scope looks like, keeping it below 5.

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?

Two sentences, no filler: the first front-loads what is returned and in what order, the second carries the trigger and the permission scope. Every clause earns its place.

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 parameters, rich annotations and an output schema already present, the description needs only to supply scope, ordering and auth. It does all three, so an agent can call it correctly without further inference.

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 tool takes zero parameters, so there is no parameter semantics to add and the baseline of 4 applies. Nothing in the description misleads about inputs.

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 the resource precisely ("the orders of the person you act for"), plus ordering ("newest first") and the exact fields returned (item bought, listing, week, paid status). It is unambiguous about what it returns, but it never explicitly contrasts itself with the nearest sibling, list_my_listings, so an agent must infer orders-vs-listings on its own.

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 after start_checkout to see when they've paid" gives a concrete trigger condition tied to a named sibling, which is real routing guidance rather than vague context. It stops short of stating when-not-to-use or what to do instead when no checkout has occurred.

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