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

Annotations already declare readOnlyHint=true, and the description adds non-obvious behavioral context the annotations cannot: the account-level access requirement and the fact that authentication must happen through the client rather than start_login. It stops short of 5 because nothing is said about scope of the returned metrics (per-key vs account) or history limits beyond the schema.

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 functional sentence is front-loaded and the auth prerequisite is separated into its own block. The ACCESS block is slightly verbose for the value it carries, but every sentence is actionable.

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 metrics tool with two well-documented optional params and no output schema, the description covers what the tool returns and the access gate. Remaining gaps (return shape, default period behavior) are minor and partly covered by annotations.

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%, so both parameters (months, period) are already fully documented in the schema. The description adds no format, precedence, or interaction guidance between months and period, so the 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?

Specific verb+resource ('Get usage metrics for the authenticated account') followed by the concrete content returned (verification counts, API calls, quota usage). It doesn't differentiate itself from similar siblings like get_api_key_usage or get_platform_summary, so it stops short of a 5.

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 ACCESS block gives a real prerequisite (a Proof account plus client authentication) and usefully warns that start_login does NOT unlock this tool. However, it never states when to prefer this tool over the closely related usage/subscription siblings, leaving the primary selection question unanswered.

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