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

Annotations already establish readOnly/idempotent/non-destructive behavior, so the description mainly adds scope ('Covers all US carriers registered with FMCSA') and return categories. It does not clarify that calling with neither dot_number nor mc_number is likely invalid, even though the schema marks both optional. No contradiction with annotations.

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?

Information-dense and front-loaded with the core lookup, followed by a useful field inventory, usage examples, and scope. The examples are slightly redundant, but the description remains focused and earns its length.

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 two-parameter lookup with no output schema, the description is mostly complete: it lists return fields, identifiers, and coverage. The main gaps are the lack of an explicit at-least-one-parameter constraint and route to sibling FMCSA tools, which prevents a top score.

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?

The schema provides property names and integer types but no descriptions; the description supplies the domain meaning (DOT/MC are carrier identifiers) and says the lookup is by one or the other. It stops short of documenting exact accepted formats or explicitly stating that at least one parameter is required.

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 a specific action ('look up') on a defined resource class (trucking/freight/motor carrier) keyed by DOT or MC number, and enumerates returned fields. It does not explicitly name or exclude nearby siblings like fmcsa_carrier_search, fmcsa_carrier_authority, or fmcsa_carrier_compare, so differentiation is implicit rather than explicit.

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 gives explicit query-phrase examples ('is this carrier safe?', 'check this DOT number') that tell an agent when to invoke it. However, it never says when not to use it or mentions alternatives for narrower or comparative carrier lookups.

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