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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the description does not need to restate those. It adds valuable context beyond annotations: the required UCP-Agent identification and the conditional presence of messages, continue_url, and order.

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 description is concise, front-loaded with the main purpose and possible return states, and includes the important authentication requirement in a single additional sentence. Every element 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?

Given the full output schema, complete parameter descriptions, and annotations covering safety traits, the description provides the essential behavioral and authentication context needed for correct invocation. Nothing critical 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 description coverage is 100%, and both parameters have clear descriptions in the schema. The description adds a small amount of context by emphasizing the required UCP platform identification, but the schema already carries most of the semantic weight.

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 states a specific verb and resource: it returns the current state of a UCP checkout session by id, enumerates the possible states, and lists the fields that may be returned. This clearly distinguishes it from sibling mutation tools like create_checkout, update_checkout, complete_checkout, and cancel_checkout.

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?

Usage is implied: it queries a checkout session by id created by create_checkout, and the required meta['ucp-agent'] identification is stated. However, there is no explicit guidance about when to use this tool instead of the checkout mutation siblings, though their semantics make the distinction fairly obvious.

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