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

Annotations already declare readOnlyHint, idempotentHint, and destructiveHint, covering safety. The description adds a valuable behavioral quirk: commas are treated as separators, so users must type 1200 instead of 1,200. This goes beyond the schema and annotations, giving agents critical parsing behavior. No contradictions.

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 sentences with no wasted words. The purpose is front-loaded, followed by input format and a practical gotcha. The source URL is extra but not distracting. The description is efficient and well-structured.

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 simple one-parameter read-only tool with an output schema and full annotations, the description covers purpose, input format, and a parsing pitfall. Nothing an agent needs to invoke it correctly is missing. The output schema handles return values, so no need to describe them.

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% and the schema describes the parameter as 'A list of numbers separated by spaces, commas, semicolons or new lines'. The description repeats this but adds a crucial caveat about thousand separators, which prevents misinterpretation. This adds meaning beyond the schema, so it exceeds the baseline of 3.

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 description states a specific verb ('Work out') and a clear resource (a list of numbers) and enumerates the exact outputs: mean, median, mode, sum, count, minimum and maximum. This is unambiguous and distinguishes it from other calculators like standard_deviation_calculator.

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 description clearly implies when to use the tool (when you need central tendency and summary statistics) but does not explicitly mention alternatives or exclusions. It provides input formatting guidance, which is helpful for parameter usage, but no when-not-to-use criteria. The context is clear, but no explicit routing.

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