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

readOnlyHint=true already establishes this as a safe read. The description adds only that quantities are aggregated per window, but says nothing about window-size limits, sampling, pagination, or auth scopes — gaps that matter for a metrics-style endpoint.

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 tight sentences with the outcome front-loaded and the endpoint reference trailing. The 'Polar: GET /v1/meters/{id}/quantities' fragment is somewhat redundant but conventional and does not bloat the definition.

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 must carry the return shape, and it only says 'aggregated quantities' — it does not indicate that results are bucketed by the interval parameter or what fields each bucket contains. Adequate to call the tool, incomplete to interpret the response.

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 100%, so meter_id, start/end_timestamp, interval, and customer_id are all documented in the schema. The description adds no syntax, format, or default detail beyond that, so 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?

The description gives a specific verb ('Fetch the aggregated quantities') and resource ('a meter'), and adds the business framing that these quantities drive usage-based billing. It is distinguishable from siblings like polar_list_meters or polar_get_metrics, though it never explicitly names the alternative it is not.

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?

Usage is only implied: the billing-charge framing suggests when this result matters, and the tool name/required params make the scenario obvious. There is no explicit when-to-use vs polar_get_metrics or polar_list_meters, and no stated prerequisites or exclusions.

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