prompt_stats

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

The description discloses that the tool is 'cheap' (implying low cost), that it does no time analysis, and that day/week bucketing uses UTC timestamps rather than local time. It also explains the semantics of omitting until ('up to now'). With no annotations provided, the description carries the burden and does a good job, though it could mention pagination or 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?

The description is dense but well-organized, front-loading the core purpose and the key alternative. Every sentence adds value: the group_by constraint, the time format spec, and the return shape are all necessary. No filler or repetition.

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?

The description covers purpose, alternatives, parameter semantics, timezone behavior, and return shape. The output schema exists, so the return format note is a helpful summary rather than a requirement. For a 3-parameter tool with no annotations, this is complete.

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 0%, so the description must fully compensate. It does: it explains the allowed values for group_by, the accepted formats for since/until, the meaning of relative durations, and the behavior of omitting until. This is far beyond what the bare schema provides.

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 opens with a specific verb and resource ('Cheap prompt counts and character totals') and immediately distinguishes itself from the sibling time_summary tool. It clearly states what the tool does and what it does not do, making it easy for an agent to select it correctly.

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 description explicitly says to use time_summary instead when the question is about time, providing a clear alternative. It also gives detailed guidance on the group_by values and the since/until formats, including examples and the meaning of relative durations. This is comprehensive usage guidance.

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