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

Annotations already declare readOnlyHint, idempotentHint, and non-destructive behavior. The description adds value by disclosing that the tool returns aggregated totals plus a time-series breakdown, which is behavioral context beyond what annotations provide. There is no contradiction with 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?

The description is compact and well-structured: a clear one-sentence purpose, a short when-to-use, useful combination hints, and a brief output format. Each section is purposeful and no information is redundant or wasted.

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?

Despite lacking an output schema, the description includes an explicit output format ('Totals + time-series breakdown'), which covers the main return-value gap. Combined with usage guidance and annotations, this is a complete and self-sufficient description for a read-only reporting tool.

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?

Input schema covers 100% of parameters with descriptions and enums, including defaults for period and granularity. The description only restates 'Supports period filtering and granularity control' without adding new semantic detail, so it stays at the schema-covered baseline.

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?

Description clearly states 'Get aggregated performance report for a media buy' and lists specific metrics (spend, impressions, clicks, conversions) with a time-series breakdown. This is a specific verb+resource combination that distinguishes it from sibling tools like get_compliance_status and list_media_buys.

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 <when_to_use> section explicitly says 'To check campaign performance metrics after activation' and mentions period/granularity controls. The <combination_hints> further clarifies the workflow by pairing list_media_buys → get_campaign_report and suggesting get_compliance_status for a full overview, giving clear context and alternatives.

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