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

Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds the backing endpoint (GET /items/units), which signals a static reference list, but says nothing about return shape, pagination, or whether the list is firm-specific.

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 short fragments, zero waste, with the highest-value fact (what these units are used for) front-loaded. Slightly telegraphic but nothing needs cutting.

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 simple one-parameter read-only reference lookup with no output schema, this is enough to select and call the tool correctly. A note on whether the response is a flat value list or objects with ids would make it 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?

Schema coverage is 100% and the single 'language' parameter has an enum plus a clear description in the schema itself. The description adds no meaning about how language affects the returned unit names, 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 names the resource (units of measure) and, more usefully, states its role: the values accepted as quantity_unit on items and invoice lines. It is not confused with any sibling, though it omits an explicit verb (the title supplies 'List').

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?

By saying these are the accepted quantity_unit values, it implies when to call it – as a lookup before creating or updating items/invoice lines. It never states that explicitly, nor does it exclude any case or name an alternative.

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