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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false, so safety is covered structurally. The description still adds genuine behavioral context beyond them: it names the exact payload fields and explicitly rules out any write path for money, directing top-ups to the human via billing_url.

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, no filler, and the returned-fields summary is front-loaded ahead of the 'no top-up' constraint. Every clause carries information the agent needs.

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 formatting needn't be explained, and the description still summarizes the payload in plain language. With zero parameters, full annotations, and a stated escalation path for top-ups, nothing needed to invoke it correctly is missing.

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 no parameters, so there is nothing for the description to disambiguate; the baseline of 4 applies. It correctly implies the call is account-wide rather than per-campaign or per-account-selectable.

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 concrete resource (ad account balance) and enumerates the returned fields: amount spent, spending limit, remaining budget, and the platform billing link. That makes the tool's scope unmistakable, though it doesn't explicitly differentiate itself from lookalike siblings such as get_ad_caps or ads_overview.

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?

Gives an explicit boundary: no app can add money, so an agent seeking to top up must surface billing_url to a human rather than call anything. That is a real when-not rule, but there's no guidance on when this is preferable to get_ad_caps or get_account for adjacent spend questions.

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