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

Annotations already declare this a read-only, idempotent, non-destructive open-world call, so the safety profile is covered. The description's real addition is the comparison behavior ('already compared with the same number of days before') and the response shape (account total first, then per-campaign rows including budget-limited campaigns). It does not state what happens when there is no prior-period data or how the comparison baseline interacts with THIS_MONTH/LAST_MONTH periods.

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?

It is a single dense sentence, front-loaded with the headline promise ('Every campaign in one call') followed by the payload contents. The colon-list is compact and every element earns its place, though the sentence is long enough that the account-total-then-campaigns structure is slightly buried mid-clause.

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, so the description must carry the return-value burden, and it does list the returned sections and metrics. It leaves gaps around edge cases (campaigns with zero spend, missing prior period, how periods map to the comparison window), but for a read-only reporting tool with full schema coverage this is largely sufficient.

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 all three parameters, the enum values, the default, and the manager-account requirement documented directly in the schema. The description adds nothing about the period parameter or its interaction with the comparison window, so 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?

The description names a concrete resource (every campaign) and enumerates the exact metrics returned: spend, conversions, cost per conversion, movement, daily budget, and budget-limited campaigns. It is specific enough that an agent knows what it will get, but it never distinguishes this from siblings such as account_overview, client_report, or find_wasted_spend, whose names overlap with the account-total and lost-impression content described here.

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: an agent can infer this is the tool for campaign-level performance over a period, and 'every campaign in one call' hints that it favors breadth over filtering. There is no explicit when-to-use, when-not-to-use, or named alternative among the many siblings that produce performance or waste reports.

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