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

Annotations already indicate this is a non-readonly, non-idempotent, non-destructive, closed-world mutation. The description adds no behavioral context beyond the property target, such as permission requirements, side effects, or whether repeated calls create duplicates.

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 purpose is front-loaded in a single clear sentence, but the trailing "Tools revision: 5c9bea8f." adds no task-relevant value. The description is concise but too sparse for the tool's complexity.

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?

This is a five-parameter mutation with zero schema description coverage. Although annotations cover basic safety and an output schema exists, the input semantics are essentially undocumented, leaving the agent under-equipped to call it correctly.

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%, and the description provides no explanation of the five parameters. It does not clarify the difference between parameter_name and display_name, the meaning of scope, or valid measurement_unit values.

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 states a specific verb and resource: "Create a custom metric on a GA4 property." This is clear enough to distinguish creation from update/list siblings, but it does not distinguish custom metrics from the closely related ga4_create_custom_dimension.

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?

There is no guidance on when to use this tool versus ga4_create_custom_dimension, ga4_update_custom_metric, or ga4_list_custom_metrics. It also omits prerequisites such as required GA4 permissions or property scope.

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