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

Annotations declare readOnlyHint=false, destructiveHint=true and idempotentHint=true, but the description adds nothing about what is actually destructive or what happens to fields not listed in the update mask. For a destructive mutation, the description should explain the blast radius or that unlisted fields are preserved; instead it only carries a build-revision string.

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 operational sentence is short and front-loaded, but the trailing 'Tools revision: 5c9bea8f' is pure noise that consumes attention without informing invocation. Brevity here reflects under-specification rather than disciplined editing.

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 destructive, idempotent mutation with three undocumented parameters and no schema descriptions, the description should cover required permissions, resource-name format, and the meaning of the update mask. An output schema exists, so return values need not be explained, but the input-side gaps are substantial.

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%, so the description bears the full burden, yet it only hints that 'name' is a resource name. The critical 'update_mask' parameter (default 'displayName') and 'display_name' are completely undocumented, leaving the agent to guess the resource-name format and mask syntax.

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 (update a custom metric) and indicates it works by resource name, but says nothing about which properties can be changed or how it differs from ga4_update_custom_dimension or the create/list siblings. The agent can grasp the operation class but not its scope.

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 when-to-use guidance at all: no note that the metric must already exist, no pointer to ga4_create_custom_metric or ga4_list_custom_metrics as the alternatives, and no mention of prerequisites such as property permissions. The agent must infer everything from the name.

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