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

Annotations already declare readOnlyHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds the useful framing that values are 'observed' (data-dependent, not a static catalog), but it never says whether results are bounded by time range or how large the value set can be — notable given idempotentHint=false implies results may vary between calls.

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 compact sentences, front-loaded with the action and followed by the motivation and a concrete example. Little waste; only the trailing 'before running query_insights' phrasing is slightly padded.

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, so return values need no explanation, and the tool is a simple read with zero required parameters. The remaining gap is parameter coverage — event_kind and the source enum are undocumented anywhere — but everything needed to attempt a call is present.

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 only 25% (only project_id is described), so the description must compensate and it only partly does: the '$country' example implies the property_key format, and 'event or user property' loosely maps to the source enum. event_kind and the four PROPERTY_SOURCE_* values are left entirely unexplained.

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?

Specific verb and resource: 'lists the observed values of an event or user property', with a concrete example ('$country') that pins down what a value looks like. It does not distinguish itself from the similarly named sibling get_activity_property_values, so an agent must infer the split from names alone.

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?

Provides clear context: use it to populate filters and breakdowns with real values before running query_insights. That routes the agent to the right workflow stage, but there is no explicit exclusion or comparison against the activity-side equivalents.

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