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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint. The description adds the credential dependency, warning that a `credentials_required` error will be returned until credentials are provisioned, which is valuable behavioral context beyond the annotations.

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 sentences, both purposeful: one describes the core function, the other a relevant operational caveat. No redundant words.

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 only 2 parameters and rich annotations, the description addresses the main functionality and the credential error. It does not specify return structure, but no output schema exists, and the phrase 'full item detail' hints at the return. Adequate for the tool's simplicity.

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 covers both parameters with descriptions, including the required comma-separated item_ids with max 20 and the optional country enum. The description merely reiterates the schema details without adding new semantics, so 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 uses a specific verb 'Bulk-fetch' and identifies the resource 'full item detail for up to 20 eBay items in a single call', clearly distinguishing from the singular sibling tool get_ebay_item. The title reinforces the batch capability.

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?

The description implies batch usage with 'Bulk-fetch' and 'up to 20', but does not explicitly contrast with get_ebay_item or specify when not to use. There are no alternative tool references or exclusions.

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