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

Annotations already declare non-readonly, destructive, and non-idempotent behavior, so the description adds useful context beyond them: these variables are OFF by default, disabling causes silent failure, confirm=false previews, and publishing is required afterward. It does not discuss permissions, reversibility, or the risk of enabling all variables, leaving a small transparency gap.

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 front-loaded with purpose and failure impact before the workflow details. The unformatted comma-separated list of 28 built-in variable names is long but earns its place because the schema provides no type description, though it could be more structured.

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?

An output schema exists, so return values need not be explained, and annotations carry the safety profile. The description covers why and how to use the tool plus the publish dependency, but container and workspace parameter semantics are absent, which is a minor completeness gap for an otherwise rich definition.

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 must compensate. It thoroughly explains the required types parameter (comma-separated with examples and a common-variable list) and the confirm preview flag, but it omits any explanation of container and workspace, leaving two parameters semantically undocumented.

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 ("ENABLES GTM built-in variables") and immediately lists examples, making clear it targets built-in variables rather than custom GTM variables. It is readily distinguishable from siblings such as create_gtm_variable or update_gtm_entity.

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?

It gives a strong usage scenario (disabled built-in variables silently prevent trigger/tag firing) and describes the preview workflow via confirm=false plus the follow-up publish_gtm_container step. It stops short of explicitly naming alternative tools or when not to use it, so it is clear but not exhaustive.

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