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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the description needs to add context beyond that. It explains the tool returns a linear end-of-month projection based on daily average, which is valuable behavioral detail. No contradictions with annotations.

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 sentences: the first lists what the tool returns, the second provides the recommended use case. No unnecessary words, information is front-loaded. Excellent conciseness.

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 fully explains what the tool does and its output. An output schema exists (though not shown), so return values are covered. The tool is simple with no parameters, and the description is complete enough for an agent to understand its usage without ambiguity.

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?

The tool has 0 parameters, and schema description coverage is 100%. Per the rubric, baseline is 4 for 0 params. The description doesn't need to explain parameters, but it does explain the output fields (usage, limit, percentage, projection), which adds value.

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 clearly states the tool returns monthly call usage data, plan limit, percentage used, and a linear projection. It specifies the resource (calls) and the action (get usage), making the purpose unmistakable. While it doesn't explicitly distinguish from siblings, the unique combination of usage data and projection sets it apart.

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 provides a clear use case: 'Use to spot when an org will hit its cap.' It does not explicitly state when not to use or list alternatives, but the use case is concrete and helpful. Sibling tools like 'get_today_cost' or 'estimate_cost' serve different purposes, so the guidance is adequate.

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