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

readOnlyHint=true already establishes the safety profile, so the description only needs to add return-content context; saying it yields 'carrier ids' does that minimally. It says nothing about whether the list is static or account-scoped, or the id format, which would be the genuinely additive details.

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 short fragment with no waste, but it is under-specified rather than concise — a single complete sentence stating that it returns the set of valid carrier ids would cost no more space and be clearer.

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 carries the burden of explaining the return value; 'carrier ids' is a start but leaves format (array of strings?), stability, and scope unstated. For a trivial no-param lookup this is adequate but not complete.

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 tool takes zero parameters, so the schema-coverage baseline is a 4. The description does add cross-tool value by naming the 'carrier' parameter these ids feed into, which the schema alone cannot 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?

The description is a noun phrase, 'Carrier ids that can be passed as carrier,' which conveys the resource (carrier ids) but not an explicit verb or what the call actually returns. It does implicitly separate this from track_package/track_packages as a reference lookup rather than a tracking action.

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?

The clause 'that can be passed as carrier' hints at the use case — populating the carrier parameter on the tracking tools — but never states when to call this versus just calling track_package directly, nor any prerequisites.

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