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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds the useful fact that results are aggregated into four named metrics rather than raw rows, but it says nothing about grouping/scope (all workspaces? per agent?), refresh behaviour, or what an empty window returns.

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?

A single front-loaded sentence with the aggregate verb first and the returned metrics trailing as a compact list. Nothing is padded or repeated.

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 does the minimum by listing the four metric names, but it never describes the response shape (field names, types, units for 'minutes'/'spend', currency) or how aggregation boundaries are determined. For a metrics tool this leaves real gaps.

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 both parameters are already documented, including the window values and the required 'purpose' compliance field. The description restates the window options already present in the schema and adds no syntax or interpretation beyond it; 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 names a specific verb ('Aggregate') and resource ('call stats') and even enumerates the aggregates produced (total, failed, minutes, spend), so the operation is unmistakable. It does not differentiate itself from neighbours like list_calls, get_call, or get_dialer_report, which is the only thing keeping it from a 5.

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 agent can infer this is the tool for summarized counts over a time window rather than per-record retrieval, but there is no explicit statement of when to choose it over list_calls/get_dialer_report or of any prerequisites. No exclusions or alternatives are named.

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