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

readOnlyHint=true already establishes this is a safe read, and the description usefully adds that results are bucketed by time and gives the REST endpoint. It does not disclose return shape, pagination behavior against the 1000-bucket limit, or whether data has retention bounds. Solid but not rich beyond the annotation.

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 sentences with the resource and scope front-loaded, followed by the endpoint. No filler and nothing repeated from the schema.

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?

With no output schema, the description carries the burden of explaining what comes back, and 'usage statistics bucketed by time' is only a gesture at the return shape (metrics present, bucket keys, retention window). Adequate for invocation but thin for interpreting results.

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% with defaults, enum options, and inclusive/exclusive bounds all documented in the schema itself. The description's 'bucketed by time' loosely relates to unit/direction but adds no format or interaction detail beyond the schema. Baseline 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?

States a specific verb (Retrieve) and resource (message/connection/channel usage statistics) and scopes it to 'the app tied to the API key', which implicitly separates it from the account-level sibling. It stops short of naming ably_get_account_stats, so the sibling distinction must be inferred from the scoping phrase alone.

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?

The API-key scoping implies this is the app-level counterpart to account-level stats, but there is no explicit when-to-use, when-not-to-use, or named alternative. An agent can guess the intent but receives no direct routing guidance.

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