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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is fully covered by structured data. The description adds nothing beyond that: it does not say the computation is deterministic, how an empty or single-element list is handled, or what the numeric result represents, so it fails to contribute any behavioral context of its own.

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 sentences, zero filler, with the statistic front-loaded and the variant detail second. It is efficient, though the brevity tips into under-specification for a statistics tool rather than being genuinely dense with 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?

An output schema exists and annotations cover the safety profile, so the description does not need to explain return values. However, for a two-parameter statistical calculator surrounded by variance/mean/median siblings, a minimum-viable definition should at least distinguish it from calculator_variance and hint at what the returned number is; that is missing.

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%: both `data` ('Non-empty list of numbers') and `std_type` (enum with default 'sample') are already documented and enumerated in the schema. The description merely echoes the enum values already present, adding no format, edge-case or meaning beyond the structured fields, so the baseline-3 rule 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?

The sentence identifies the computed statistic (standard deviation) and its two variants, but it is essentially a restatement of the title 'Standard Deviation Calculator' rather than a verb+resource statement like 'Computes the population or sample standard deviation of a list of numbers.' With ~180 sibling calculators including calculator_variance, calculator_mean and calculator_average, the description provides no differentiation from the closest neighbour.

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 only guidance is the parenthetical 'default sample', which is a default value, not a when-to-use rule. There is no statement of when to pick this over calculator_variance (a near-identical sibling) or when population vs sample is appropriate, and no prerequisites or exclusions are given.

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