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

Annotations already declare readOnlyHint and idempotentHint, so the read-only nature is known. The description adds the attribution requirement and license URL, which is actionable behavioral context beyond annotations. It does not detail error behavior for missing/multiple identifiers, but that is not required given the simple scope.

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 sentences, each earning its place: purpose with examples, sibling distinction, and licensing notice. Information is front-loaded and free of filler.

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?

Given the simple single-tool scope, an output schema exists (so return format is covered), and annotations cover safety, the description is complete. It covers purpose, usage, alternatives, and legal terms without extraneous detail.

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?

The schema already describes all five parameters with examples and clarifies that 'chinese' holds pinyin. The description adds the crucial constraint that exactly one identifier must be used, which is not captured in the schema's 'default: null' fields, helping the agent understand how to combine parameters.

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 clearly states the tool returns one of the eight trigrams using exactly one of five identifier types, with concrete examples. It also explicitly distinguishes this from list_trigrams, which returns all eight, making the purpose unambiguous.

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 directly contrasts with list_trigrams ('This returns a single trigram; list_trigrams returns all eight'), giving an explicit alternative and when-not-to-use guidance. It also instructs that exactly one identifier must be provided, which shapes usage.

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