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

Annotations already fully declare the safety profile (readOnlyHint, idempotentHint, destructiveHint=false, openWorldHint=false), so the description carries little extra burden. It adds nothing beyond that profile — no note on result count, pagination, or whether built-in variables appear in the response. The 'Tools revision' line is metadata, not behavioral context.

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 front-loaded and tight, stating exactly what is listed and where. The second sentence is an internal build revision string that provides no value to an agent deciding how to call the tool, so it fails the 'every sentence earns its place' test.

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. What is missing for a single-parameter lookup tool is the workspace identifier format and any note on pagination or result limits — the two things an agent would actually get wrong.

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% for the single 'workspace' parameter, so the description must compensate and it largely doesn't. It tells the agent the call is scoped to a workspace, but not whether the value is a numeric workspace ID, a path like accounts/X/containers/Y/workspaces/Z, or a display name.

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?

Specific verb (List) and resource (variables) with an important scope qualifier: 'user-defined' and 'in a workspace'. The 'user-defined' qualifier is what distinguishes this from the sibling gtm_list_built_in_variables, but it does so implicitly rather than naming the sibling.

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?

The phrase 'user-defined' implicitly signals this is not the tool for built-in variables, and the requirement to scope to a workspace is conveyed. However there is no explicit when-to-use statement, no mention of gtm_list_built_in_variables as the counterpart, and no note about prerequisites such as needing container/workspace IDs.

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