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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, so the description need not repeat those. It adds value by listing the metrics included and the default month behavior. No contradiction with annotations; the description is consistent with a read-only, idempotent operation.

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 a single, information-dense sentence that front-loads the action and resource, then lists metrics efficiently. It contains no filler or redundant phrasing, making it highly concise while still being complete.

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?

Given the presence of an output schema and annotations covering safety and idempotency, the description provides sufficient context: it states what is included, defaults, and scope. Nothing critical is missing for an agent to invoke the tool correctly, though it could mention that both year and month default to current values (but the schema already does that).

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 coverage is 100%, and both parameters (year, month) are fully described in the schema with their defaults. The description only repeats the month default and adds no new parameter semantics beyond what the schema already provides, so it meets the baseline but does not exceed it.

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 states a specific verb ('Get') and resource ('monthly Chasync performance statistics'), and enumerates the exact metrics included (leads, emails sent, opens, etc.), making it unambiguous. There are no sibling tools for statistics, so it naturally distinguishes itself.

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 description provides clear context that the tool returns monthly statistics and defaults to the current month, which implicitly tells the agent when to call it (when account performance data is needed). There are no alternative statistics tools, so no explicit exclusions are required, but it lacks an explicit 'when not to use' statement.

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