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

Annotations already establish readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds genuine behavioral context beyond that: results come from Mercari itself ('Mercari's own') and are returned in upstream relevance order, not sorted or re-ranked locally. No auth, rate-limit, or pagination detail, but for this tool that is minor.

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?

One sentence, zero filler, and the key qualifier (partial keyword) and ordering behavior are both front-loaded.

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 autocomplete utility with an output schema (so return values need no explanation) and annotations covering safety, the description supplies purpose, input intent, and result ordering. Only explicit guidance on full-query alternatives 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?

With one parameter and 0% schema description coverage, the description must compensate. It does clarify that the query is a 'partial keyword' rather than a complete search phrase, which is real added meaning, but it gives no format, length, or language guidance. 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?

States a specific verb+resource: returns Mercari's search-suggestion list. The phrase 'for a partial keyword' distinguishes it from mercari_search (which takes a full query), so the agent can tell the two apart without opening schemas.

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 'partial keyword' framing implies the typeahead use case, which is useful context, but there is no explicit when-to-use statement, no when-not-to-use, and no named alternative (e.g. mercari_search for full queries). Usage is implied rather than stated.

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