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

Annotations already declare readOnly, idempotent, non-destructive and openWorld, so the safety profile is covered. The description adds a genuine caveat that nutrition/allergen data stays per-label rather than being normalised across the comparison, but the wording ('remain specific to each label') is vague and no other behavioral detail (e.g. what happens with out-of-stock items) is given.

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 waste, with the resource and the compared dimensions front-loaded before the caveat. Nothing could be removed without losing 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?

For a simple read-only comparison tool with no output schema, stating the compared dimensions effectively substitutes for return-value documentation. The one gap is that result shape and behaviour for unavailable beers are unstated, but overall it is sufficient to call correctly.

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?

There is a single 'ids' parameter with zero schema description coverage, but the enum of valid beer slugs is present in the schema. The description only restates the 2–4 count constraint that minItems/maxItems already enforce, and hints that ids are 'specific' beers — marginal added meaning.

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?

Uses a specific verb (Compare) on a specific resource (2–4 IMPOSSIBREW beers) and enumerates the comparison dimensions: flavour, pack prices, availability, source descriptions. This implicitly separates it from compare_pack_value (value only) and compare_alternatives, though no sibling is named 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?

The '2 to 4 specific ... beers' phrasing implies usage for a known, small set of products, which is a usable constraint, but there is no explicit when-not guidance and no routing to browse_beers or compare_alternatives. Usage must be inferred.

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