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

Annotations already declare readOnly, idempotent, non-destructive, closed-world, so the safety profile is covered. The description adds genuinely non-redundant behavior: it requires a key, and the delivery portion of the response is only present once the order is paid, which tells the agent an absent delivery field is not an error.

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?

Three short sentences with zero filler: scope first, sibling routing second, prerequisite last. Nothing repeats the annotations and nothing could be cut without losing information.

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 one-param read with rich annotations this is nearly complete, and since no output schema exists the brief sketch of the return (status, conditional delivery) does useful work. A one-line note on unknown-id behavior would close the remaining gap.

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?

With a single parameter at 100% schema description coverage, the schema already documents the id, its origin (buy or my_orders) and the "or_…" format. The description only restates "by order_id" and adds no constraints or format detail of its own.

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?

States a specific resource and selector ("One order by order_id") and what the response contains (status, and delivery once paid). It explicitly contrasts with the sibling my_orders, so an agent can separate the single-order read from the list read without opening either schema.

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?

Names the alternative explicitly — "To list all your orders use my_orders" — which is exactly the routing decision an agent faces here. It also flags the auth prerequisite ("Needs your key"), though it gives no guidance on failure cases such as an unknown or other-user order_id.

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