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

With no annotations, the description carries the full burden and does disclose the single most important behavioral trait: this call does not initiate or pay a transaction, i.e. it is a safe non-mutating read despite the "buy" name. It stops short of stating auth requirements, side effects, or what the directions look 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?

A single sentence with no filler, front-loading the actual behavior and the critical non-mutation disclaimer. Every clause 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?

For a one-parameter tool with no output schema, the description establishes purpose, safety profile, and the source of the product ID (via the schema). Return content is only loosely characterized as "directions," which is a minor gap but adequate given the tool's simplicity.

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?

Only one parameter with 100% schema description coverage; the schema already explains it is a kebab-case product ID from list_products. The description adds no further parameter meaning, so the baseline of 3 applies.

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 resource and outcome ("purchase directions for a product") and immediately negates the misleading implication of the name by saying it does not initiate or pay a transaction. It distinguishes itself from a real purchase action, though it does not contrast with siblings like preview_product or list_products by name.

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?

The negative clause ("without initiating or paying a transaction") implies the usage context — retrieve instructions rather than execute a purchase — but it never states when to prefer this over preview_product or list_payment_methods, or any prerequisite. Usage is inferable rather than stated.

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