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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so safety is covered; the description's '[read-only]' tag is redundant. However, it adds real value beyond the annotations by disclosing the underlying endpoint (GET /api/v2/ads/accounts) and, importantly, that balance figures are in minor units and ready-state is included — since no output schema exists, this is the only signal about the return payload.

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 lines with the return attributes front-loaded and the endpoint parenthetical kept short. The bracketed '[read-only]' prefix duplicates the annotations and is the only wasted token.

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?

For a zero-required-param read tool, the essentials are present, and since there is no output schema the mention of currency/spend limit/balance/readiness usefully sketches the return shape. It stops short of saying whether results are paginated or cover multiple ad accounts per brand, which an agent would want to know before relying on the output.

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% and the single brandId parameter is fully documented there, including the 'personal' value and the 403 behavior for brand-bound keys. The description adds no parameter meaning of its own, so the baseline of 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?

It names the resource (the brand's ad account) and enumerates the returned attributes: currency, spend limit, balance in minor units, readiness. That is specific enough to distinguish it from campaign or insight tools, though the singular phrasing ('the brand's ad account') slightly understates that it is a list, and it does not differentiate from the close sibling ads_readiness.

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?

There is no when-to-use, when-not-to-use, or alternative routing guidance. An agent reading this cannot tell whether to call ads_accounts_list vs ads_readiness, ads_campaigns_list, or list_connected_accounts; the only context (brand-bound keys, 403 behavior) lives in the schema, not the description.

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