metadata_get_resource_metadata

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

Annotations include readOnlyHint=true, so safety is covered. The description adds context about field naming conventions ('metrics.' and 'segments.' prefixes) and that responses should be cached as they don't change frequently. This adds behavioral context beyond the annotation without contradicting it.

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 four sentences, with the main purpose in the first sentence and supporting details following. There is no fluff—every sentence contributes either functional purpose, usage guidance, or caching advice.

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?

Given an output schema exists, there's no need to explain return values. The description covers scope, usage, mandatory invocation, field naming, and caching. For a single-parameter tool with rich schema/annotations, this is complete and self-sufficient.

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 has 100% coverage for the single parameter, which already explains it as 'The name of the Google Ads resource (e.g., 'campaign', 'ad_group').' The description repeats this with examples but doesn't add substantially new semantic detail, so 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 clearly states the tool retrieves selectable, filterable, and sortable fields for a specific Google Ads resource, including compatible metrics and segments. It uses a specific verb ('Retrieves') and resource, distinguishing it from siblings like search and mutation tools.

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 tells when to use it: to discover fields before constructing a query for the `search` tool. It also provides a strong exclusion: 'Do not guess fields, you MUST use this tool to discover them.' This is clear guidance on when this tool is required vs alternatives.

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