Retrieve a checkout session by your reference

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

Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description still adds real behavioral value by disclosing the failure mode for an unknown reference ('404 resource_missing') and the 'unique per mode' scoping of references — information an agent cannot get from the annotations.

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?

Very short and front-loaded, with the 404 behavior placed immediately after the core statement. The opening sentence duplicates the title and the second sentence restates 'retrieve a checkout session by the reference', so a small amount of the text is redundant rather than additive.

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 single-parameter, read-only lookup with rich annotations and no output schema, the description covers what the tool does, the key semantics, and the not-found behavior. It is nearly sufficient; only the sibling alternative for ID-based lookup is absent.

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 the parameter's type and meaning are already documented. The description goes beyond that by clarifying the reference is the one supplied at creation and is unique per mode, which matters for constructing a valid lookup key across test/live modes.

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 verb and resource ('Retrieve a checkout session') and qualifies it by lookup key ('by the reference you gave'), which separates it from the ID-based 'get_checkout_session' sibling. It stops short of naming that sibling explicitly, so the differentiation is inferable rather than stated.

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 only implied: the agent must already hold the reference it supplied at creation time. There is no explicit when-to-use/when-not-to-use guidance and no pointer to 'get_checkout_session' for agents that only have the session ID, which is the most likely wrong-tool confusion among the siblings.

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