Metadata Get Resource Metadata

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

Annotations already declare readOnlyHint=true, so the description correctly aligns with that. It adds behavioral context beyond the annotation: field name prefixes ('metrics.' and 'segments.'), the relationship to query construction, and that responses should be cached because they don't change frequently. No contradiction or hidden side effects.

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 well-structured and front-loaded with the core function, followed by usage guidance, a mandatory instruction, and caching advice. There is minor redundancy between the first sentence's 'including compatible metrics and segments' and the later sentence repeating that metrics/segments are returned, but overall every sentence contributes.

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 tool is simple (one fully documented parameter, read-only annotation, output schema present), and the description covers what the tool returns, how to use it, why it must be used before `search`, and caching behavior. Nothing an agent needs to call it correctly is missing.

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 schema already covers the only parameter fully with a description and example. The description reinforces the example ('campaign', 'ad_group') but does not add much beyond what the schema provides. With 100% schema_description_coverage, 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') with a clear resource ('selectable, filterable, and sortable fields for a specific Google Ads resource') and explicitly mentions metrics and segments. It distinguishes itself from the sibling `search` tool by framing itself as the discovery step before querying.

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 gives explicit when-to-use guidance: 'Use this tool to find out which fields you can select, filter by, or sort by when querying a specific resource.' It also states a hard rule: 'Do not guess fields, you MUST use this tool to discover them before constructing a query for the `search` tool.' This clearly routes an agent to the correct workflow.

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