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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds real context beyond them: these are pre-saved, account-scoped definitions whose fields are interpreted (numerator_scope, denominator_metric, denominator_scale, revenue_source_ids). It does not mention result count or pagination, which keeps it below a 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?

Three dense sentences, front-loaded with the core definition before field semantics and routing. Every clause carries information, though the stacked parentheticals make it slightly harder to scan than a strictly minimal version would be.

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 job of explaining return values and does so for the key item fields, plus it links to query_unit_costs for computation. Remaining gaps — list shape, whether an empty set is possible, ordering — are minor but real.

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?

With zero input parameters the baseline is 4, and the description goes further by explaining the semantics of the fields returned on each item — notably that denominator_scale is a readability factor limited to 1/1000/1000000 and that revenue_source_ids names revenue streams. That compensates for the absence of an output 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?

States a specific verb and resource ('List this account's saved unit-economics metrics') and immediately defines what such a metric is ('a cost ÷ business-unit ratio'). It also implicitly separates itself from the sibling query_unit_costs, which computes values rather than listing saved definitions.

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?

Routes the agent to two alternatives with conditions: 'see list_cost_tags' for tag_value scoping and 'Pass an id to query_unit_costs to compute one over a date range'. The guidance is clear but framed as follow-on actions rather than an explicit 'use this when you want definitions, use query_unit_costs when you want numbers' exclusion.

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