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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds genuinely useful context beyond that: it scopes the data to the *current* schedule and lays out the returned payload (hierarchy, all three duty columns, units, footnotes, Chapter 99 cross-references, child lines). It does not say what happens when a code is valid-format but absent, or whether lookups are cached/rate-limited.

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?

A single front-loaded sentence with the verb and subject first, followed by the accepted input forms and then the return payload. Every clause carries information; nothing is repeated from the title or annotations.

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 no output schema, the description must and does enumerate the return shape, which is the right use of its budget for a simple 2-parameter read tool. The remaining omission is failure behavior for unmatched codes and whether truncated "summary" output flags truncation, a minor gap rather than a blocking one.

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 parameters are already documented in the schema, including the summary/full enum and its 25-vs-150 line effect. The description restates the accepted digit lengths and dot tolerance without adding syntax, normalization, or default behavior beyond the schema, so the baseline 3 applies.

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 gives a specific verb ("looks up") plus a precisely bounded resource (one HTS code in the current HTUS), and enumerates exactly what comes back. The singular "one HTS code" implicitly contrasts with the sibling hts_search, so an agent can tell this is a by-code retrieval rather than a query search.

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 rather than stated: the reader infers "call this when you already have an HTS code" from the required-format detail and the singular scope. There is no explicit exclusion such as "if you only have a product description, use hts_search instead," which is the main misselection risk given the sibling set.

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