Metadata Get Resource Metadata

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

The annotation readOnlyHint=true already covers the safety profile, and the description complements it by disclosing the response contents (fields, metrics, segments) and the naming convention for metrics/segments. It also adds an operational trait: 'responses ... should be cached, as they don't change frequently'. No contradiction with annotations.

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?

The description is front-loaded with the core purpose and adds concise, actionable guidance. There is minor redundancy: the first sentence says 'including compatible metrics and segments' and the third sentence repeats that metrics and segments can be selected. Still, it is well-structured and every section adds value.

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 metadata-lookup tool with an output schema and readOnlyHint annotation, the description covers everything an agent needs: what the tool returns, naming conventions, mandatory usage before querying, and caching guidance. No significant gaps remain for correct invocation.

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 input schema already describes both parameters comprehensively (100% coverage), so the description need not repeat them. It adds a small amount of extra context with examples like 'campaign', 'ad_group', but this does not significantly exceed what the schema provides. Baseline 3 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 uses a specific verb ('Retrieves') and names a clear resource: the selectable, filterable, and sortable fields for a Google Ads resource, including metrics and segments. This clearly distinguishes the tool from the siblings: search_search executes queries, while this tool provides metadata for building them.

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 description explicitly states when to use the tool: before constructing a query for the `search` tool, and it warns 'Do not guess fields, you MUST use this tool to discover them'. This gives the agent an unambiguous directive and contextual placement relative to the sibling search tool.

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