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

Annotations already declare readOnly, idempotent, non-destructive and open-world, so the safety profile is covered. The description adds genuinely new behavior: result ordering ('best match first') and a cost model (free within the daily allowance, then $0.003 USDC per call via x402), which an agent must know before repeated calls.

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?

Two sentences, no waste, front-loaded with the return value and examples before the billing caveat. Every clause earns its place.

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?

An output schema exists, so return-value detail is unnecessary, and annotations cover the safety profile; the description supplies ordering and pricing on top. The only meaningful omission is routing guidance relative to the sibling commodity/heading lookup tools.

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 description coverage is 100%, so both q and limit are documented in the schema, and the baseline is 3. The description reinforces q's intent with sample product descriptions, but says nothing about limit or result-shaping beyond what the schema already states.

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 exactly what comes back — candidate commodity codes, headings and chapters — and anchors it to a free-text product description with two concrete examples. It is clearly a description-based search, distinct from the code-lookup siblings (uk-trade-tariff__commodity, uk-trade-tariff__heading), though it never names those alternatives to draw the boundary explicitly.

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?

Usage is implied: supply a product description when you don't yet know the code. There is no statement of when not to use it, no mention of routing to uk-trade-tariff__commodity/heading once a code is known, and no prerequisites (e.g., what happens when no candidate matches).

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