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

Goes well beyond the annotations by disclosing error semantics: invalid input never raises a protocol error and instead returns an {"error": ...} object with a fix hint, plus the caveat field in the response and the retry-safety implication. The read-only/idempotent restatement is redundant with annotations but harmless.

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?

Front-loaded with the core verb and the FREE signal, then the caveat and error contract. Slightly padded by the example output and a sentence restating annotation-provided read-only/idempotent traits, but nothing is materially wasteful.

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, yet the description still shows a sample response and flags the caveat field, and it fully covers the failure mode. An agent has everything needed to call this correctly and interpret the result.

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%, so the schema already documents units, length, width, height and weight. The worked example (48x40x36, 400 lb -> 40 cu ft, 10.0 pcf, class 100) adds concrete meaning by showing how the inputs combine into density, which the schema alone does not convey.

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: derive a US LTL freight class from density. The domain is narrow and clearly separable from siblings like dim_weight or rate_card, though no sibling is named 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?

Explicitly says when to use it (a first estimate before a carrier quote) and when not to (not as a final classification), and explains why: NMFC also weighs stowability, handling and liability so carriers reclassify. That is a genuine when/when-not pair with rationale.

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