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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint=false and destructiveHint=false, so the safety profile is fully covered by structured data. The description's contribution is the content inventory (which measurements come back), which is useful given there is no output schema, but it says nothing about data source, completeness, or units.

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?

It is a single sentence, front-loaded with the resource, which is efficient in structure. But it is a densely packed run-on list of instruments and measurements that is tiring to parse and could be broken into a purpose clause plus a returned-fields list.

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 takes on the job of telling the agent what comes back, and it does that thoroughly — refractive index, birefringence, dispersion, SG, hardness, crystal system, instrument readings, pleochroism and spectrum lines. Grounding details such as units or whether values are ranges are missing, but the essential content inventory is there.

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% and the single parameter is a fully enumerated slug, so the schema carries the semantics by itself. The description only indirectly signals a single-stone scope ('one gemstone') and adds no detail about accepted values or format.

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 (a single gemstone) and enumerates the measured properties, so the general intent of a property lookup is clear. However, it never states a verb ('returns', 'looks up') and does nothing to separate it from siblings like absorption_spectrum, which its mention of 'lines and bands a hand spectroscope shows' actively overlaps with.

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?

There is no when-to-use guidance at all: nothing tells the agent to pick this over identify_gem (unknown stone) or compare_gemstones (multiple stones), even though the one-gemstone scope would make that distinction trivial to state. Usage is only implied by the phrase 'about one gemstone'.

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