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

Annotations alone leave the mutation's business impact ambiguous. The description clarifies that nothing is charged until a human completes checkout and discloses the main error cases: missing listing, add-on not purchasable yet, and unavailable payment configuration.

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 concise sentences with the operation, the critical caveat, and the error conditions each in their own clear slot. No filler and no repetition of schema content.

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 two-parameter tool with full schema coverage and a separate output schema, this description covers the purpose, the charge timing caveat, the human dependency, and the likely failure modes. An agent has what it needs to invoke 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 coverage is 100%, so the baseline is 3. The description adds useful business meaning such as 'one paid add-on' and 'one listing', reinforcing what the slug and product parameters represent without restating their schema text.

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 precise action verb ('Create'), an exact object ('a Stripe checkout URL'), and a narrow scope ('for one paid add-on on one listing'). It also clarifies the output's target ('for a HUMAN to open'), making the tool's role distinct from sibling tools.

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?

Gives clear context: this tool produces an uncompleted checkout link and must not be presented as a finished purchase. It does not explicitly name alternatives or exclusions, but no listed sibling tool serves the same checkout-creation role.

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