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

readOnlyHint=true already establishes this as a safe read, so the description's job is to add context beyond that. It does explain the windowed-aggregation semantics and the billing purpose, but says nothing about result size, pagination, or how many buckets are returned.

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?

One front-loaded sentence delivering purpose and business context, followed by a terse endpoint pointer. Efficient, though the API-path sentence adds little for an agent that already has the tool binding.

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 should hint at the return shape; 'aggregated quantities over a window' combined with the interval bucket-size parameter lets an agent infer a bucketed series, but the exact result structure and size limits are left unstated.

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% with all five parameters documented, so the schema carries the parameter burden and baseline 3 applies. The description's phrase 'over a window' loosely reinforces start/end timestamps but adds no syntax or format detail beyond the 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 (Fetch) and resource (aggregated quantities a meter has recorded) and adds the business meaning ('what usage-based billing will charge for'), which cleanly separates it from polar_list_meters and polar_get_metrics. The endpoint reference confirms the exact resource being read.

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 billing framing implies when an agent would want this (usage aggregation over a window), but there is no explicit when-to-use/when-not guidance and no named alternative such as polar_get_metrics for cross-meter metrics. Usage is inferable rather than stated.

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