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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=true, so the safety profile is covered. The description adds the output metric set and 'highest spend first' ordering, but says nothing about return volume, truncation when limit is hit, or multi-account behavior (accountId required only when the sign-in reaches multiple accounts is buried in the schema, not the description).

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 dense sentence, front-loaded with the resource and scope before the metric list. It is efficient, though the metric enumeration is slightly long and pushes the ordering note to the end rather than leading with it.

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?

With no output schema, the description usefully enumerates the returned metrics, which is the key thing an agent needs to know. Defaults and formats live in the fully-described schema, and annotations cover safety. Only missing pieces are truncation/limit-hit behavior and multi-account scoping, which are minor 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?

Schema description coverage is 100%, so all five parameters (limit, startDate, endDate, accountId, campaignId) are fully documented with defaults and formats in the schema. The description only reconfirms the date-range and optional-campaign dimensions without adding format, default, or edge-case meaning beyond the schema. Baseline 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?

States a specific resource (ad group performance) and enumerates the exact metrics returned (impressions, clicks, CTR, average CPC, cost, conversions, cost per conversion), plus implicit scope (date range, optional campaign) and ordering. An agent can distinguish it from msads_get_campaign_performance or msads_get_keyword_performance only by inference from the resource noun; no sibling is named.

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?

Usage is only implied by the scope phrase 'optionally one campaign' and the date-range mention. There is no explicit when-to-use-this-vs-alternatives guidance, and no mention of when the campaignId filter should be applied versus aggregating across the account.

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