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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so the safety profile is covered. The description adds only a 'cost: 1 credit' billing note, which is genuinely useful, but says nothing about edge behavior an agent needs here: empty list handling, non-numeric strings, the output format, or whether the string input form is comma-separated.

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?

One sentence plus a cost tag, with the core purpose front-loaded and no redundant wording. Every clause carries information.

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, annotation-covered, no-output-schema tool, the description is close to sufficient. The remaining gap is input-shape handling (how a string of numbers is parsed) and empty-input behavior.

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 coverage is 100%, so the single 'numbers' parameter is already documented including requiredness and unit. The description restates that it is a list of numbers but adds no clarity on the schema's ambiguous anyOf (raw array vs a string), which is exactly where extra prose would help.

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?

States a specific verb and resource ('Calculates the arithmetic mean ... of a list of numbers') and even gives the algorithm, which implicitly separates it from siblings like calculate_median or calculate_standard_deviation. It stops short of naming those siblings explicitly, so differentiation relies on the reader inferring it from the term 'arithmetic mean'.

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 explicit when-to-use or when-not-to-use guidance and no named alternatives among the many math siblings (calculate_median, calculate_standard_deviation, calculate). Usage is only implied by the precise definition of what it computes.

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