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

With no annotations, the description carries the full burden of behavioral disclosure. It adds useful context ('hourly time-series', includes both cost and call count), but does not state data ordering, timezone, inclusion of partial hours, or any response shape. Acceptable for a simple read-only-style query tool, but several traits are left implicit.

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 tight sentences with zero filler. The core definition is front-loaded, and the second sentence gives practical usage context without redundancy.

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?

For a one-parameter read tool with a clear output concept ('hourly time-series of cost and call count'), the description is nearly sufficient. It lacks explicit sibling differentiation and output details, but the schema covers the parameter and the description covers the return shape sufficiently.

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 the days parameter is fully documented in the input schema with range and default. The description itself adds no extra parameter-specific meaning, so the baseline of 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?

Description uses a specific verb ('Get') and resource ('hourly time-series of AI/LLM cost and call count'), clearly distinguishing this trend-focused tool from sibling summary or log tools. The example questions further pin down its purpose.

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?

Provides clear context through the questions 'is my AI spend trending up?' and 'when did my AI costs spike?', signaling trend/spike analysis use cases. However, it does not explicitly name alternatives like get_cost_summary or get_ai_summary, nor give when-not-to-use guidance.

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