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 useful content beyond that by naming the returned counters and their daily granularity, but says nothing about date-range defaults, the agent breakdown option, or result size/limits.

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 tight sentence with no filler; the return contents are front-loaded and nothing is wasted.

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 convey the return shape, and it does so at a basic level (daily send/receive/API counters). Combined with the fully documented input schema and safety annotations, an agent has enough to call it, though the breakdown dimension and date-window behavior go unmentioned.

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%, including date defaults, ID sourcing hints, and the breakdown enum, so the schema carries parameter meaning entirely. The description only echoes the daily granularity and counter types, adding little 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?

Specific verb ('Returns') and specific resource ('send, receive and API counters for one domain'), with granularity ('daily') stated. The 'one domain' scoping implicitly separates it from org_usage and agent_usage, though those siblings are never named.

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?

No when-to-use guidance, no prerequisites, and no explicit routing between this and the closely related org_usage/agent_usage tools. The agent must infer from the tool name which usage scope it needs.

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