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

Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is covered. The description adds nothing beyond that — it doesn't mention edge cases such as mode returning multiple values, empty input, or the 10,000-element cap. Adequate but not value-adding with annotations present.

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 short lines, purpose front-loaded in the first sentence and the operation set placed immediately after. Nothing is redundant or padded for a tool of this simplicity.

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?

With a 100%-covered two-parameter schema and an existing output schema, return values need not be described. The definition is nearly complete; only edge-case behavior for degenerate inputs is unaddressed, which is a minor gap for a pure calculation tool.

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% and both parameters are documented in the schema with examples and allowed values. The description's operation list merely repeats the enum values already present in the schema, adding no syntax or format detail beyond it. Baseline 3 is appropriate.

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 ('Perform statistical calculations on a list of numbers') and enumerates the supported operations, so the agent knows exactly what the tool computes. It is distinguishable from calc_expression and the matrix_* siblings by domain, though it never names those alternatives explicitly.

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?

Usage is implied by the operation list and 'on a list of numbers', but there is no explicit when-to-use/when-not guidance or routing to calc_expression for arbitrary expressions. The agent must infer that this tool is for descriptive statistics over an existing numeric array rather than for evaluating formulas.

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