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

readOnlyHint=true already covers the safety profile; the description adds that the data includes period-over-period delta comparisons and lists the returned metrics. It does not discuss rate limits or auth, but for a read-only report tool the annotation plus metric list is sufficient context.

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 tight sentences, front-loaded with the metric list and a separate delta-comparison behavior note. No filler or redundant restatement of the schema.

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, but the description names the returned metrics and the delta feature; date defaults live in the schema. The ambiguous periodDays parameter and absence of sibling guidance leave some gaps for an agent deciding how to parameterize the call.

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?

Only startDate, endDate, and campaignId are described in the schema (60% coverage); required brandId has no schema description and periodDays has none. The tool description adds general date-range semantics but does not explain what periodDays controls or how brandId scopes results, so it fails to compensate for the coverage gap.

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 an explicit verb ('Fetch') and resource ('Microsoft Advertising performance data') and enumerates the exact metrics returned. The title and name make the Bing Ads scope unmistakable, distinguishing it from generic sibling report tools like get_campaign_report.

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 establishes clear context: use this when Microsoft Advertising performance metrics over a date range are needed. It does not name alternatives or state exclusions, so differentiation from sibling tools leans partly on naming rather than explicit guidance.

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