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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered and the description only adds the downstream purpose of the result. It says nothing about result size, ordering, truncation, or scoping behavior beyond the schema, so genuine behavioral context is thin.

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?

A single well-formed sentence with the core action front-loaded and the usage rationale immediately after. Nothing is redundant and the parenthetical examples are compact.

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 read-only lookup with 7 parameters (5 required) and no output schema, the description covers what the tool returns conceptually ('distinct values') but omits how many values come back, whether results are bounded, and how the optional event/search parameters shape output. Adequate but leaves real gaps for a multi-scope query tool.

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 description coverage is 100%, so every parameter including the enums for kind and dataType is already documented in the schema; baseline 3 applies. The description's value examples (country codes, platform names, item ids) add only illustrative color, not new meaning for any parameter such as the optional event or search filters.

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 gives a specific verb and resource: 'Discover distinct values for a specific event property or argument', and even clarifies the two lookup modes (property vs argument) that map to the 'kind' enum. It is clearly distinct from siblings like list_event_types or describe_event_types, though it never names those alternatives.

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 states a concrete when-to-use condition: 'use before building string or number filters to know which values exist', which tells the agent to call this as a discovery step prior to filter construction. It stops short of explicit when-not guidance or naming sibling tools to use instead.

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