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

Annotations already declare readOnlyHint and idempotentHint, so safety is covered. The description adds value beyond that by explaining the matching precedence (exact, alias, prefix/word), the return payload scope, and the fallback of three nearest suggestions when no match occurs.

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?

Three compact sentences cover purpose, matching behavior, return content, and no-match fallback. The main action is front-loaded, and every sentence contributes necessary operational detail without redundancy.

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 read-only single-parameter lookup with no output schema, the description is complete: it tells the agent what input is expected, how matching works, what a successful response contains, and what happens on failure. No critical operational gap remains.

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%, and the single parameter already includes a helpful description with examples and a case-insensitivity note. The tool description reinforces the matching behavior but does not add meaning beyond what the schema provides, so a baseline 3 is appropriate.

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 states a specific verb and resource: 'Look up a single diamond or gemology term in the encyclopedia of 90 fact-checked and sourced entries.' It clearly differentiates from siblings like search_encyclopedia by emphasizing single-term lookup with exact/alias/prefix matching rather than general searching.

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 context is clear: use this when you need a dictionary-style definition of one term, and the matching behavior is spelled out. It does not explicitly name alternatives or say when not to use it, but the singular lookup framing is enough to steer an agent away from broader tools.

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