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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds useful behavioral context beyond that: it discloses the underlying API, that results are paginated, and the page ceiling of 150. Return format is left to the output schema, which is appropriate.

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?

One front-loaded sentence with zero filler; the core purpose leads and the differentiating detail follows. Nothing could be cut without losing routing value.

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?

With a 3-param schema at full coverage, readOnly/openWorld annotations, and an output schema, the definition supplies everything an agent needs to invoke it correctly. Only a marginal gap remains: no explicit tie-back to the depop_item sibling by name.

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 slug, after, and limit are already fully documented. The description's 'up to 150 per page' marginally reinforces the limit bound but adds no syntax or cursor semantics beyond the schema. Baseline 3 is correct.

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 specific verb+resource ('Items similar to a given Depop listing') and explicitly distinguishes the outcome from the sibling carousel inside depop_item detail. An agent can tell what it returns and why it differs from the adjacent feature without opening any schema.

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?

Clearly frames when to reach for this over the item detail's small carousel by contrasting richness and pagination. It stops short of an explicit 'when-not-to-use' rule or naming depop_item as the alternative, so it is clear context rather than full routing.

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