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

Annotations already declare destructiveHint=true and idempotentHint=true; the description goes beyond them by explaining exactly what is destroyed: the current name is overwritten and any field named in update_mask other than displayName is cleared or reset to default. That is precisely the hazard an agent needs to know before calling. It omits auth requirements and whether the reset is recoverable.

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 front-loaded sentences that each carry information: the operation first, then the update_mask hazard. The trailing "Tools revision: d80f65c0." adds no decision-relevant value and dilutes the otherwise tight text.

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 3-parameter mutation tool with an output schema (so return values need not be described), the definition covers operation, scope, and the main data-loss risk. Remaining gaps — resource-name format and permission requirements — are modest rather than blocking.

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?

With 0% schema description coverage, the description carries the full burden and does most of it: it explains that name is the resource identifier, display_name is the replacement value, and update_mask must be displayName or other fields get reset. The expected format of the 'name' resource string (e.g., properties/{id}/customMetrics/{id}) is never given.

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?

States a specific verb and resource ("Rename a custom metric by resource name") and narrows the scope to display_name only, which separates it from ga4_create_custom_metric and ga4_update_custom_dimension. It stops short of naming any sibling explicitly, so the differentiation is inferred rather than stated.

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?

Usage is implied — this tool is for renaming, not for changing other metric fields — and the update_mask constraint is spelled out. There is no explicit when-to-use vs. an alternative (e.g., create a new metric instead of renaming) and no prerequisites such as required property-level permissions.

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