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

With no annotations, the description carries the full burden. It discloses the effect of each operation (append, drop by 0-based index, replace full list, empty) and the customer merge behavior, plus the checkout-in-progress restriction. This gives the agent a solid behavioral model, though it doesn't cover edge cases like out-of-bounds indices or error returns.

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 sentences, each with a distinct role: purpose, operation semantics, customer behavior, and usage guidance + constraint. No filler, front-loaded purpose.

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 5-parameter tool with no output schema and no annotations, the description explains the core behaviors and provides a verification step. It could elaborate on return values or prerequisites for items, but overall it is complete enough for an agent to use the tool 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 only 20% (indices only). The description compensates by explaining the op enum values, that items are used for add/set, and that customer merges name/email/phone. This adds meaning beyond the raw schema for most parameters.

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 'Modify an open cart before checkout' — a specific verb and resource, then details each op (add, remove, set, clear) and the customer merge. It distinguishes from siblings by scoping to open carts and excluding carts with checkout in progress.

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 gives clear usage context: 'before checkout' and the constraint 'Cannot modify a cart that already has a checkout in progress.' It also advises 'Call get_cart afterwards to confirm,' establishing a workflow. No explicit alternative tool names are mentioned, but the constraint provides a when-not.

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