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

Annotations already indicate a write operation (readOnlyHint=false) and non-idempotency. The description adds context: it returns a continue_url and explicitly states it does not charge anything, which goes beyond the structured metadata and clarifies side effects.

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?

Three sentences with no fluff. The main purpose is front-loaded, followed by the return value and a safety note. Every sentence 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 simple two-parameter tool with annotations covering safety and idempotency, the description provides enough to call it: it explains the purpose, the return URL, and that no charge occurs. It lacks explicit parameter value guidance, but the schema enum covers that. Overall, it is complete for typical use.

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 0%, so the description must explain the parameters. It says 'one offer' which implies offer_id selects the offer and quantity is 1, but it does not explain the enum values (realestate-mac/windows) or that quantity is fixed at 1 due to min/max constraints. The description provides minimal semantic help.

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 a clear verb ('Start a purchase') and resource ('one offer'), and specifies the return value (continue_url). It distinguishes itself from siblings like get_checkout and list_products by focusing on initiating a checkout rather than querying or listing.

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 description implies when to use it (when starting a purchase) but does not explicitly mention alternatives or when not to use it. Siblings like get_checkout exist for checking status, but no guidance is given, so usage is only implied.

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