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

With no annotations, the description carries the full disclosure burden, and it does contribute one genuinely useful behavioral fact: the cheapest/fastest fields remain null until the dataset supports them, warning the agent not to treat nulls as errors. It says nothing about read-only nature, permissions, latency across proxies, or what the response shape looks like.

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?

Two short sentences, front-loaded with the action and followed by a caveat about null outputs; nothing is padded. The brevity is efficient, though it is arguably too terse for a tool with 13 nested item fields.

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?

This is a complex tool: five top-level parameters, a nested item object with thirteen fields, enums on two parameters, no annotations, and no output schema. Against that complexity, two sentences covering only the cart/proxy notion and a null caveat leave major gaps in how to call it and what it returns.

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?

Top-level schema coverage is 0%: country, lang, proxy, shipping_method, and items have no descriptions at the top level. The description only obliquely maps to two of them ("multi-item cart" → items, "for each proxy" → proxy) and says nothing about country, lang, or shipping_method, leaving the caller to guess the required inputs.

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 names a verb and resource ("Estimate a multi-item cart for each proxy"), which is enough to know it produces per-proxy estimates for a multi-item cart. However, "estimate" leaves the estimated quantity ambiguous (shipping cost? total landed cost? delivery time?), and nothing distinguishes it from siblings like estimate_landed_cost or check_shippability.

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?

There is no when-to-use guidance, no exclusion of alternatives, and no prerequisites (e.g. that a country and items are required). The agent must infer from the name alone that this is the multi-proxy comparison path versus the single-estimate sibling.

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