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

Annotations declare a non-read-only, non-idempotent, open-world mutation, and the description adds real behavioral context beyond that: the two-phase preview/commit pattern, the fact that nothing is booked unless confirm=true, the auth scheme (Bearer cmt_...), and the returned Comet order number. This is exactly the extra context the annotations cannot convey.

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 front-loaded sentences that each do work: purpose, call sequence, return value, credential requirement. No filler, no restatement of the title beyond what is needed.

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?

The tool is complex (30 params) but the schema carries 83% description coverage and an output schema exists, so return-shape detail is unnecessary. The description closes the remaining gaps: auth prerequisite, mandatory two-step confirmation, and where to get credentials. An agent has everything needed to call 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 description coverage is 83%, so the schema already documents nearly every parameter, including confirm, service, vehicle, when and the pickup/dropoff fields. The description reinforces the confirm gate and the preview contents but adds no syntax or defaults the schema lacks, so baseline 3 applies.

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 first sentence gives a specific verb and resource ('Book a same-day courier delivery on a Comet account') and scopes it to account holders. It is immediately distinguishable from the read-oriented siblings get_quote, order_status and recent_orders, especially since the preview-vs-confirm distinction is spelled out.

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?

Explicit when-to-use workflow: call once without confirm to get a preview, show the preview to the user, then call again with identical details and confirm=true to place the order. It also routes non-account-holders to a phone number, so an agent knows the prerequisite before invoking.

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