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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering the safety profile. The description adds value beyond that by disclosing provenance ('verified by an FGAA-qualified gemmologist') and the exact return shape ('definition, its subject section, and a citable anchor URL'). It does not disclose behavior for unknown terms, but that gap is minor given the presence of an output schema.

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, zero filler. The first sentence front-loads the action, source, verification status, and returns; the second delivers usage examples. Every clause earns its place and nothing is repeated from the schema or annotations.

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 a single required parameter, 100% schema coverage, an output schema present, and safety annotations covering read-only/idempotent behavior, the description is nearly complete. The only absent detail is behavior on unrecognized terms (e.g., error vs. empty result), which is a small gap for a simple lookup tool. The example list adds enough input guidance that an agent can invoke it correctly without further context.

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 the term parameter already described as 'The gemmological term to define,' so the baseline is 3. The description exceeds that baseline by supplying five concrete example values (padparadscha, corundum, parti sapphire, unheated, asterism), which teach the agent what constitutes a valid term — ranging from mineral names to treatments to phenomena — something the schema alone does not convey.

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 opens with a specific verb and resource: 'Look up a gemmological term in The Gem Lexicon of Ministry of Gems.' It states the returns (definition, subject section, citable anchor URL) and gives concrete example terms (padparadscha, corundum, asterism) that bound the scope. The examples and the phrase '215 definitions' clearly differentiate this curated-lexicon lookup from siblings like search_gem_knowledge or list_gem_terms.

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 gives clear when-to-use context: 'Use for terms such as...' with five example terms spanning mineral names, color varieties, and phenomena. It does not explicitly name alternatives or exclusion conditions, so an agent must infer from sibling names (e.g., list_gem_terms for browsing, gem_properties for physical data) rather than being told. Clear context but no explicit exclusions earns a 4.

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