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

Annotations already declare readOnlyHint/idempotentHint/destructiveHint=false, so the safety profile is covered; the description adds real value by disclosing the return shape (value/label pairs) and the label fallback logic from account_customers to raw id. It also notes the REST endpoint it mirrors. No rate limits or auth notes, so not a full 5.

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 sentences, front-loaded with the core action and scope, followed by return-shape detail. Every clause adds information (purpose, follow-up tool, output semantics, endpoint) with no 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?

With no output schema, the description usefully explains the returned value/label entries, which is exactly what an agent needs without a schema. The main remaining gap is date-range parameter format/semantics, which is left undocumented.

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 0%, so the description must compensate, and it only partly does. It clarifies the allowed dimension values ('metric' or 'external_customer_id'), but those are already constrained by the schema enum, and it says nothing about start_date/end_date format or whether they are optional.

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 and resource ('List the distinct values seen for a usage dimension') and scopes it over a date range, directly distinguishing it from the query tools. An agent can tell this discovery/list tool apart from siblings like query_usage without opening any schema.

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?

Explicitly frames the use case: 'useful for discovering filter values before calling query_usage', which routes the agent to the right follow-up tool. It lacks explicit when-not-to-use guidance or naming of the alternative list_dimensions sibling, keeping it short of a 5.

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