Discover GA4 dimensions and metrics

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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint, and destructiveHint=false, so the safety profile is covered. The description adds value beyond that with the compatibility caveat, which is a genuine behavioral limitation not captured in annotations. It is concise but meaningful.

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 with no filler: the first states what the tool does, the second states a critical limitation. Both sentences earn their place, and the key verb-resource pair is front-loaded.

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?

The description covers purpose and the principal caveat, and rich annotations handle the safety profile. But gaps remain: the limit parameter is unexplained, and the boundary with ga4_list_custom_dimensions is not drawn, which matters since both tools touch custom definitions.

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 0%, so the description carries the full burden for parameter meaning. It only implicitly references propertyId ('for a property') and says nothing about the limit parameter, leaving its semantics entirely to inference. The description does not compensate for the schema gap.

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 uses a specific verb ('Discover') and names the resource precisely: valid GA4 field names, descriptions, and custom definitions for a property. It clearly positions the tool as a pre-reporting metadata lookup. However, it does not differentiate from the sibling ga4_list_custom_dimensions, and the mention of 'custom definitions' partially overlaps with that sibling's purpose.

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?

'before reporting' provides clear contextual guidance on when to call this tool, and the caveat 'Does not guarantee every combination is compatible' tells the agent not to treat returned fields as freely combinable in report queries. It stops short of explicitly naming alternatives or exclusion conditions.

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