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

Annotations already cover the safety profile (readOnlyHint, destructiveHint, openWorldHint), so the description is free to add behavior it uniquely knows: readings are ordered newest first, labels are ordered by largest total, and series results are summed per bucket with a week default. It does not mention result-size limits or pagination on the readings array.

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 what-it-returns clause is front-loaded, followed by usage triggers, then parameter mechanics; every sentence carries distinct information with no filler. Density is high but appropriate for a tool with five parameters and no output 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 correctly describes the return payload (definition, readings, open decisions, labels, series) and its ordering. It omits how many readings are returned or whether they are capped, which is a minor remaining gap for a read tool.

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 the baseline is 3, but the description earns more by explaining that metricId accepts either an id or a snake_case slug, and by giving concrete slice/by examples ('new users in DE', 'new users by country') plus the interaction with bucket. That adds interpretive value beyond the schema's field-level text.

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 (read one metric) and enumerates exactly what is returned: definition fields, readings newest-first, and open decisions bound to it. It is clearly distinguishable from ledger_metrics_list, since it also explains that metricId can come from that sibling.

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?

Gives explicit trigger conditions: 'Use before answering how is X trending?' or before recording a reading against it, which routes the agent away from list/create siblings. It stops short of stating when-not-to-use it or naming the recording tool outright, so it falls just 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.