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

The readOnlyHint annotation already covers the read-only safety profile, so the description's main added transparency is the account-id resolution behavior from ABLY_ACCOUNT_ID and the Control API endpoint. It does not describe return format, error behavior, or pagination, but for a straightforward read-only stats call the added context is adequate.

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?

The description is two sentences with no filler. The core purpose is front-loaded, and the additional endpoint and account-resolution details each contribute useful context without redundancy.

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 read-only statistics tool with fully documented parameters and no output schema, the description covers the main action, scope, time bucketing, and account resolution. It does not detail the exact metrics returned, but given the tool's simplicity and the readOnlyHint, the missing return specification is a minor gap.

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%, so all five parameters are already documented in the input schema. The description adds minor value by explaining the account_id defaulting behavior via the ABLY_ACCOUNT_ID environment variable, but it does not add meaningful semantics beyond 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?

The description names a specific verb ('Retrieve'), resource ('aggregated usage statistics across the whole account'), and a key behavioral detail (bucketing by time). It clearly conveys the account-level scope, which helps distinguish it from related stats tools, though it does not explicitly name or contrast the closest sibling.

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?

No guidance is given about when to prefer this tool over alternatives. The phrase 'across the whole account' implies account scope, but the description never mentions ably_get_stats or any other sibling to clarify the boundary. It also does not state when not to use it or what prerequisites apply.

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