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

Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely useful behavior beyond that: it returns `undefined` rather than throwing when the payload shape is missing, which is exactly the kind of error-behavior detail an agent needs to write defensive code. It does not describe caching or network-failure behavior, but the key failure mode is disclosed.

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 sentences, no filler, and the payload-location caveat is front-loaded. The service path is a bit dense but it is the evidence that justifies the tool's existence, so it earns its place.

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 and no parameters, the description carries the burden of explaining the return value, and it only partially does so: it says what happens on a missing payload but never states what is returned on success (presumably the measurement-system identifier). The location and failure-mode context is good, but the success shape is left to inference.

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 there is nothing for the description to disambiguate; baseline 4 applies. The description spends its space on scope and return behavior instead of inventing parameter detail, which is appropriate.

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 identifies the resource (`measurementSystem`) and its location on `/userprofile-service/userprofile/user-settings`, and explicitly distinguishes it from the social profile, which differentiates it from siblings like get_user_profile. It frames itself as 'a convenience accessor, not a data endpoint', which tells an agent it is a shortcut rather than a full fetch. It never directly states the return value (e.g., the metric/imperial preference), so it is clear but slightly indirect.

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 'not on the social profile' note implicitly steers an agent away from profile tools toward this one, and 'convenience accessor, not a data endpoint' hints at when it is preferable to a full settings fetch. However, no sibling tool is named as an alternative and there is no explicit when/when-not guidance.

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