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

Annotations already declare this a read-only, idempotent, non-destructive, closed-world call, so the safety profile is covered. The description adds a genuinely important constraint beyond the annotations: caps are raised only by a human on the Ads page, never by an agent, which tells the agent this tool can never be a path to increasing budget. It does not add rate-limit or freshness details, but the key behavioral rule is stated.

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 sentences, front-loaded with what is returned, followed by the one constraint that changes how an agent should act. No filler, no restatement of the name or annotations.

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?

An output schema exists, so return values need not be explained, and the description still summarizes them (caps, month-to-date spend, remaining room). The scope note "across all platforms" removes ambiguity about aggregation. The only gap is that it never tells the agent where this fits relative to ad_account_balance or set_ad_budget.

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?

The tool takes zero parameters, and the schema is fully covered, so there is no parameter semantics to explain — baseline applies. The description correctly spends no words on inputs.

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 the resource precisely: the day and month spend caps (across all platforms), this month's spend, and the remaining room — an agent knows exactly what it gets back. It stops short of explicitly distinguishing itself from the sibling ad_account_balance, which is the one tool most likely to be confused with it.

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 spend caps every change must fit" implies a pre-flight check before any ad mutation, which is real but indirect guidance. There is no explicit when-to-use, no when-not-to-use, and no sibling alternative named (e.g., ad_account_balance for balance vs. caps).

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