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

Annotations only supply readOnlyHint, and the description carries the real behavioral weight: the exact billing formula (graduated $10/$8/$7 with a $99 five-mailbox minimum, per provisioned mailbox, deprovision lowers billed quantity), what each activationState value actually means, and the critical warning that 'pending_provisioning' sends are sandbox previews that 'DON'T leave'. That is unusually useful disclosure.

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?

Front-loaded with the field inventory and tight throughout; each clause adds a distinct fact. It is a single very dense paragraph, and the billing and state-semantics sections might read better as separate blocks, but there is little genuine filler.

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-parameter, read-only, no-output-schema tool, the description supplies everything an agent needs: the full field set, null semantics ('vertical' null, teardown null unless canceled), billing math, and the state machine that determines whether sending is real.

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 there is nothing for the description to document beyond the schema (baseline 4). It correctly spends its words on return-field semantics instead of inventing parameter guidance.

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 (account) and enumerates the exact fields returned (brand, plan, status, vertical, billingState, activationState, counts, usage, quota, deliverability, teardown). The retrieval verb is only implied by 'overview', but sibling differentiation is explicit ('Use metrics for counts, infrastructure_status for per-mailbox health'), so an agent can place it correctly.

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?

It routes to two siblings with the condition that selects them ('Use metrics for counts, infrastructure_status for per-mailbox health') and tells the agent which field to trust ('trust activationState over sent counts'). There is no explicit 'when not to use this' statement, but the context is clear.

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