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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety burden is lifted. The description adds the conversion unit (French degrees) and hints that output includes threshold bands, but the literal '{thresholds}' placeholder is an unfilled template, so the disclosure is only partial.

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, front-loaded with the essential verb-resource-unit. The only blemish is the raw '{thresholds}' placeholder, which reads as a broken template rather than deliberate brevity.

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, so return values need not be described — but the description still injects a broken '{thresholds}' token that undercuts itself, and the unrelated 'cuisine' pointer adds noise. For a trivial 2-param, 0%-coverage compute tool, this is adequate but not clean.

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 0%, so the description must carry parameter meaning; it names the two inputs but adds nothing on granularity or accepted ranges beyond what the parameter names (calcium_mg_l, magnesium_mg_l) already imply. The units are only inferable from the names, not from the description text.

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 ('Calculate water hardness'), names the output unit ('French degrees'), and enumerates the two inputs ('calcium and magnesium concentrations'). An agent can distinguish this from the ~350 sibling calculators (e.g., water bill, water intake, pool chlorine) without opening any schema.

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 'See list_bundles for related cuisine calculators', which is a registry cross-reference, not when-to-use/when-not-to-use for this tool. It also looks misplaced — water hardness has no obvious cuisine relationship — so it may actively mislead an agent choosing between hydration/cooking/water calculators.

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