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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds genuinely new behavioral context: this hits a dedicated similar-items API and is paginated at up to 150 per page, unlike the non-paginated carousel. It doesn't cover auth or rate limits.

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?

A single tight sentence that front-loads what the tool returns and then justifies why it exists alongside the sibling. No filler.

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. The pagination depth is disclosed, but for a 0%-coverage parameter set the cursor/limit usage an agent needs to iterate pages is missing, leaving a real gap.

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 0%, so the description must compensate for three params (slug, after, limit). It only indirectly touches 'limit' via 'up to 150 per page' and says nothing about the 'after' cursor or slug format, leaving the API's pagination contract largely undocumented.

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?

Names a specific verb+resource ('items similar to a given Depop listing') and differentiates itself from the sibling carousel inside item detail. It's clear what it returns, though the sibling is referenced descriptively rather than by tool name.

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 a comparative reason to pick this over item detail's built-in similar-items carousel (richer, paginated, up to 150/page), which is enough context to route correctly. No explicit when-not or precondition guidance, but the selection rationale is clear.

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