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

Annotations already declare readOnly/idempotent/closed-world, so safety is covered. The description adds real value beyond them by disclosing the return shape (six statistics computed at once) and that per-statistic working is shown, including an explanation of why mean and median differ — useful for a tool with no output schema.

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?

Front-loaded with the action and the payoff, and the second clause justifies the value of seeing the working. The trailing marketing URL is the only low-value element, but the definition stays to two compact sentences.

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 single-parameter, read-only, idempotent calculator with no output schema, the description covers inputs, computed outputs, and the explanatory framing well enough to invoke it correctly. Edge-case behavior (invalid or empty input, very long lists) is unaddressed, which is acceptable but not 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?

Only one parameter and schema description coverage is 100%, so the separator syntax (commas, spaces, new lines) and the default list are already fully documented in the schema. The description adds nothing about input format or limits (e.g., the 100000-char cap), so baseline 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?

Specific verb-plus-resource: ingests a pasted list of numbers and returns mean, median, mode, range, sum and count in one pass. It enumerates the outputs, which implicitly separates it from stat siblings like standard_deviation_calculator or percentage_calculator, but it never names or contrasts an alternative.

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?

"Paste a list of numbers" implies the input context, and the six-in-one output hints at bulk summarization rather than single-value math. However, there is no explicit when-to-use/when-not guidance and no routing to sibling calculators for related needs such as standard deviation or percentages.

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