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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety baseline is covered. The description goes further by naming the specific side effects it avoids — no capability execution, no entitlement, no receipt — which tells the agent this call consumes nothing and mutates no account state. It stops short of describing cost, rate limits, or what the preview contains.

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?

Two short sentences, zero filler, with the most decision-relevant fact (FREE, read-only) front-loaded. Nothing is repeated from the structured fields.

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?

An output schema exists, so return values need no explanation, and the single required parameter is fully specified by the schema. For a one-param read-only preview, the description supplies the essential non-side-effect guarantee; only the routing against sibling tools is missing.

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 100% and the single item_id parameter is fully documented in the schema (including provenance from offers.list), so the description is not obliged to restate it. It adds no format or constraint nuance beyond the schema, so the baseline 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?

The description names a concrete action (preview of a 'result-shape') and asserts a key property ('never executes'), but the object of the preview is left implicit — an agent must infer from the schema that it previews the result shape of the capability referenced by item_id. It does not clearly distinguish itself from execution.preflight or capability.get, which appear to live in the same problem space.

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?

Signaling 'FREE' and 'never executes' implies this is the cheap, safe alternative to actually running a capability, so the usage is implied rather than stated. There is no explicit when-to-use/when-not versus execution.preflight, capability.get, or requirements.check, which are the most plausible siblings an agent would weigh against it.

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