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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive), so the description's job is to add beyond that – and it does: result ordering (cheapest in stock first), the presence of price/stock/shipping/link per row, and the honesty caveat that state shipping coverage is 'when known'. It does not say what happens with an unrecognized slug or whether shops outside the US are included, which keeps it short of a 5.

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 for what it returns, one for the argument source – both front-loaded and free of filler. Nothing here could be cut without losing information.

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 an output schema present, return-value explanation is unnecessary, and the description covers ordering, per-row contents and the data-quality caveat. The only gap is failure behavior for a bad slug and whether coverage is US-only, which are minor for a read-only lookup.

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-or-URL format, so the baseline would be 3. The description earns the extra point by naming the upstream tools that produce a valid value, which is real meaning the schema cannot express.

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?

Names a concrete resource (every shop listing one specific bottle) and pins down the scope and ordering ('cheapest in stock first'), plus the fields returned. That distinguishes it from search_bottles/recommend_bottles (discovery) and best_price (a single best price rather than the full shop list).

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?

It tells the agent where the argument comes from ('from search_bottles or recommend_bottles'), which is genuine pipeline guidance. But there is no explicit when-to-use versus when-to-use-an-alternative statement, e.g. against best_price or ships_to, so selection between the price/availability siblings is left to inference.

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