compare_performance

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is covered. The description adds useful behavioral context ('Calculates percentage changes and highlights significant differences'), but says nothing about return format, significance thresholds, or how the two periods map to output.

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?

Three short sentences, front-loaded with the core action and scope. No filler, though the third sentence is somewhat promotional rather than informational.

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?

There is no output schema, and the description only vaguely gestures at results ('percentage changes', 'significant differences') without explaining the structure of the comparison output. For a nested-object, 4-required-param comparison tool, the safety annotations carry the rest, making this adequate but not complete.

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%, so accountId, comparisonType, and both period objects are already fully documented in the schema. The description adds no syntax or format detail beyond what the schema provides, 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 gives a specific verb ('Compares') and concrete resources ('two time periods, campaigns, or campaign groups'), which distinguishes it from the single-scope siblings like get_campaign_performance. It stops short of explicitly naming a sibling to route against, so it is clear but not maximally differentiating.

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?

'Essential for reporting on performance trends' implies when the tool is useful, but gives no explicit when-to-use/when-not guidance and names no alternative (e.g., get_campaign_performance for single-period views). Usage context is only implied.

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