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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, so safety is covered. The description still adds genuinely new behavioral facts beyond them: it requires the 'account-read' scope and it explicitly reassures the agent that calling it will not create a charge or modify the account, which matters for a billing-adjacent tool.

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?

One dense sentence enumerating the payload, followed by a non-mutation guarantee and the scope requirement. No filler, and the key content is front-loaded.

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 enumerating return fields in the description is partly redundant, but it usefully helps selection. Auth scope and non-mutation semantics are covered; only the relationship to sibling billing tools 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 zero parameters, so the baseline is 4 and there is nothing for the description to disambiguate. The description correctly implies the org context is implicit rather than passed in.

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 specific verb ('Read') and resource ('this organization's usage') and enumerates the exact metrics returned: segment/audience totals, 30-day delivery count, rated spend in cents, projection freshness, compute-ceiling percentage. That specificity makes it hard to confuse with the write/mutation siblings, though it never names the adjacent billing siblings (check_balance, check_topup_status) explicitly.

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 by the read-only framing and the scope requirement; there is no explicit 'use this when you need X instead of check_balance/check_topup_status' routing. An agent can infer it is the aggregate usage snapshot, but the choice among billing-related tools is left to inference.

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