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

Annotations already declare readOnlyHint=true, idempotentHint=true, openWorldHint=false and destructiveHint=false, so the safety profile is fully covered without prose. The description adds that the result is a set of named tests with the tool that shows each one, but says nothing about error cases such as passing the same gemstone twice.

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?

One sentence, front-loaded with the resource and purpose, then the property list. The parenthetical glosses ('doubling of back facets, polariscope', 'fire') aid interpretation, though the sentence is dense enough that a reader must parse carefully.

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 no output schema, the description compensates by enumerating the compared properties, so the agent knows what a call returns. For a two-parameter, closed-world, read-only comparison tool this is close to sufficient; only duplicate-input behavior is unaddressed.

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% with enumerated slugs for both parameters, so the schema carries the semantics. The phrase 'two gemstones side by side' is consistent with gemstone_a/gemstone_b, but the description adds no format or edge-case guidance beyond what the enum already states.

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 names the resource (two gemstones) and the operation (a side-by-side comparison yielding discriminating tests), and enumerates the exact properties compared: refractive index, birefringence, specific gravity, dispersion, hardness, pleochroism, spectrum. That is specific enough to distinguish it from identify_gem and gem_properties, though it never names a sibling 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 closing sentence gives a concrete triggering question ('how do I tell diamond from moissanite?'), which tells the agent exactly which user intents should route here. It stops short of stating when NOT to use it (e.g. a single unknown stone, which would be identify_gem).

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