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

Goes far beyond the annotations: it discloses permance ("Meta has no API to close or delete an ad account"), a quota ("a portfolio may only hold a few"), field immutability (currency and time zone cannot be changed later), and exact idempotency semantics (a repeated key returns the first result). This is behavior an agent could not infer from readOnlyHint/destructiveHint/openWorldHint.

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?

Three sentences, each carrying distinct high-value information (scope, permanence/confirmation, idempotency), with the action front-loaded. No filler or restatement of the title.

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?

Adequately complete for a permanent, irreversible create with no output schema: the agent learns the required inputs' source, the confirmation requirement, and retry safety. It omits what the call returns (e.g., the new account id), which is a minor gap since no output schema exists.

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?

With only 43% schema description coverage the description must compensate, and it does for the highest-risk fields: idempotencyKey retry behavior, currency/timezone immutability, and the source of businessId. It does not add meaning for name or the accountId/profileId defaults, leaving those to the schema.

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 verb+resource ("Create an ad account") and scopes it precisely to "a Business portfolio from ads_list_businesses," naming the sibling that supplies the required businessId. This cleanly distinguishes it from ads_update_account, ads_get_account, and ads_list_accounts.

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 clear prerequisites and a strong operational directive: fetch the businessId via ads_list_businesses and "confirm every field with the user first." It stops short of an explicit when-not rule, but the usage context is unambiguous.

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