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

Annotations already indicate readOnly and idempotent behavior; the description adds valuable context beyond annotations: offers are always labeled 'Sponsored', listing is always free, and early-bird access results in purchasable=false. No contradiction found.

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 three sentences with no filler, front-loaded with the verb and resource, and the parenthetical field detail adds value without bloating the text.

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 zero-parameter, read-only listing tool with an output schema and strong annotations, the description fully covers purpose, workflow relationship to create_checkout, and the early-access caveat. No meaningful gaps remain.

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 tool has zero parameters and the schema coverage is trivially 100%, so the no-parameter baseline of 4 applies. No parameter explanations are necessary.

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 begins with a specific verb and resource — 'List the optional paid add-ons' — and clarifies exactly what is returned (name, effect, price). It also distinguishes from the sibling create_checkout by positioning this as the pre-checkout lookup tool.

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 clearly says 'Call this to see what's purchasable before create_checkout,' giving an explicit workflow usage cue. It also notes an early-access exclusion where offers are not purchasable, though it does not explicitly contrast with other sibling tools.

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