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

The annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so the safety profile is covered. The description adds the useful fact that results are limited to user-defined variables in one workspace, but says nothing about pagination, result ordering, or whether inherited/synced variables from other containers appear.

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 first sentence is tightly scoped and front-loaded, which is good. The second sentence, "Tools revision: d80f65c0.", is an internal version stamp that consumes space without helping the agent decide or call.

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?

The presence of an output schema and annotations means the return shape and safety profile need not be explained, so the definition is adequate for a simple single-parameter list tool. The gaps are the workspace identifier format and the lack of routing guidance toward the built-in-variable sibling.

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 schema description coverage at 0% and only the title "Workspace" on the single required parameter, the schema gives almost nothing. The description's "in a workspace" only confirms the parameter identifies a workspace; it never states the expected identifier format (e.g. accounts/{a}/containers/{c}/workspaces/{w}) or whether workspace names are accepted.

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?

Names a specific verb and resource ("List user-defined variables") and scopes it to a workspace. The qualifier "user-defined" implicitly separates it from the sibling gtm_list_built_in_variables, though that sibling is never named.

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 explicit when-to-use or when-not-to-use guidance. Usage is only implied by the phrase "user-defined," which suggests the agent should reach for gtm_list_built_in_variables when built-in variables are wanted, but this inference is left entirely to the reader.

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