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

Annotations already provide readOnlyHint=false, openWorldHint=true, idempotentHint=false, and destructiveHint=false. The description adds valuable context: it explicitly states 'This tool does not charge anything' and explains that the buyer is redirected to a Stripe-hosted page. This goes beyond the annotations and clarifies a key behavioral trait—that no payment is captured immediately.

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?

The description is two sentences, front-loaded with the core purpose, then the return behavior, and a crucial clarifying statement about not charging. Every sentence earns its place; no filler or redundancy.

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 tool with only two parameters and no output schema, the description covers the essential points: what it does, what it returns, and a key behavioral caveat. It doesn't mention error conditions or authentication, but those are not critical for this simple mutation. It is complete enough for an agent to invoke it 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?

The schema has 0% description coverage, so the description should compensate. It mentions 'one offer', which hints at the role of offer_id, but does not explicitly explain the parameters or their semantics. The quantity parameter is constrained to 1 by the schema, and the description doesn't clarify this or that it is always fixed. The description adds minimal parameter-level meaning beyond the schema, but the schema is simple enough that this is acceptable.

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 specific action ('Start a purchase of one offer') and clarifies the return value (continue_url) and the payment flow (Stripe-hosted page). This is clearly distinct from siblings like get_checkout (which likely retrieves status) and list_products (which lists offerings), so an agent can tell them apart without opening schemas.

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 the tool—when initiating a purchase—but it does not explicitly compare it to alternatives or state when not to use it. For instance, it doesn't mention that get_checkout should be used to retrieve payment status. The context is clear but lacks explicit exclusion or routing guidance.

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