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

Annotations already declare readOnlyHint=true, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds genuinely useful context the annotations do not: the shape of the returned payload (explanations, examples with pinyin/English, per-word notes, prerequisites, and follow-on points) and the input-provenance constraint. With no output schema, that return-shape disclosure earns credit beyond the annotation baseline.

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, front-loaded with the core action and slug requirement, then expected output, then routing. The return-value enumeration is long but justified given the absence of an output schema; no sentence is 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?

For a single-parameter read tool with no output schema, the description covers what is fetched, what comes back, when to call it, and where valid inputs come from. Nothing an agent needs to invoke it correctly is missing.

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 schema already documents the slug format and its origin. The description nevertheless reinforces provenance by warning not to guess a slug and naming the two tools that produce valid ones, which adds operational meaning beyond the regex and maxLength constraints.

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?

States a specific verb and resource ('Get one Mandarin grammar point by its slug') and immediately distinguishes it from its nearest sibling by tying it to search_grammar. An agent can identify this as the detail-fetch companion to the search tool without opening the schema.

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?

Gives explicit when-to-use context ('after search_grammar, when the user wants a pattern explained or wants to know what to study before it') and an explicit prohibition ('Do not guess a slug'), naming the two sibling tools that supply valid slugs. This is routing guidance an agent can act on directly.

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