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

Annotations already establish the safety profile (readOnlyHint=true, idempotentHint=true, destructiveHint=false), lowering the bar. The description adds useful behavioral context beyond annotations by stating that the tool ranks by actual returned performance ('what they actually returned') and highlights earn_per_click as the ranking key. No contradiction with 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 with no filler: the first identifies the action, resource, and output fields; the second states the decision use case and ranking priority. Both sentences earn their place, and the key information is front-loaded.

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 read-only, two-optional-parameter tool with fully documented schema and comprehensive annotations, the description covers what an agent needs: what it ranks, which metrics are returned, and when to use it. Since there is no output schema, the metric listing partially substitutes for return-value documentation. Minor omissions such as aggregation granularity are acceptable given the low complexity.

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%, with both since and until having descriptive defaults in the schema. The description adds no parameter-level semantics beyond the schema, so the baseline of 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 states a specific verb ('Rank') and resource ('merchants'), and enumerates the exact metrics returned (filtered_revenue, filtered_clicks, conversion_rate, earn_per_click, earn_per_link). This clearly differentiates it from the close sibling split_link_performance, which operates at the link level, and from split_get_earnings, which reports earnings rather than brand rankings.

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 'This is the tool for "which brands should I post more of"' provides explicit when-to-use guidance tied to a concrete decision an agent might need to make. It doesn't explicitly name alternatives or give when-not-to-use conditions, so it falls just short of a 5, but the use case is stated unambiguously.

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