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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), so the bar is lower. The description still adds genuinely useful behavior: nothing is bought until checkout, and the Shopify agent checkout endpoint does not support subscriptions, which is a real limitation an agent would otherwise miss. It stops short of detailing link expiration or multi-item failure behavior.

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?

One dense but front-loaded sentence with the return value stated first, followed by the checkout caveat. 'Read-only.' is a minor redundancy with the readOnlyHint annotation, but the rest 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 output schema, the description carries the return-value burden and does so: it enumerates the link, the line-by-line summary, and the checkout endpoint. Combined with full schema coverage and annotations, an agent has everything needed to invoke and interpret this tool.

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 baseline is 3, but the description maps the subscribe boolean to 'one-time or Subscribe and Save' and clarifies that variants correspond to the items added, which is more than the schema alone conveys. It is not fully redundant with the schema.

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 (build) and resource (cart link), plus what the returned link does: fills the shopper's cart with chosen variants, one-time or Subscribe and Save. This clearly separates it from read-only siblings like get_products and get_policies, so an agent knows this is the cart-construction tool.

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?

It ties the tool to get_products by specifying that variant_id comes from that sibling, which is the key routing context. It stops short of an explicit when-not or an alternative, but the context is clear enough to invoke correctly.

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