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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and a closed-world scope, so the safety profile is covered. The description contributes only the 2-5 ID window (already in schema) and an ambiguous claim about 'preserving unknown detailed coverage and individual sources' that does not clearly tell the agent how results are merged or what happens with unknown IDs.

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 front-loaded sentence with no wasted preamble; the source-of-IDs constraint appears early. The 'preserving unknown detailed coverage' fragment is dense and hard to parse, costing some clarity for its brevity.

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 one-parameter read-only tool with rich annotations this is close to sufficient, but with no output schema the description should indicate what the comparison returns (per-tool fields, sources, gaps) rather than alluding to it vaguely. The dependencies and error behavior on bad IDs remain unaddressed.

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 carry the load — and it does add meaning beyond the bare 'array of strings': the values must be exact catalog IDs obtained from search_gtm_tools, and the cardinality is two to five. It stops short of saying whether order matters or whether duplicates are rejected.

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 and resource ('Compare ... catalog IDs') and scopes it to two to five IDs drawn from search_gtm_tools, which separates it from the sibling search tool. The trailing clause about 'preserving unknown detailed coverage and individual sources' is opaque and blurs rather than sharpens the purpose.

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 phrase 'exact catalog IDs from search_gtm_tools' implies the prerequisite that IDs must be discovered via the sibling search tool first, which is useful. However, there is no explicit when-to-use/when-not guidance and no statement of what to do if an ID is invalid or duplicated.

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