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

Annotations already declare readOnlyHint=true and openWorldHint=true, so safety is covered. The description adds genuinely useful behavior: workspace_id must be purely numeric or the API returns {"error":"invalid_id"}, and workspace is optional in the single-workspace case. It does not mention pagination or result size behavior, which matters for a list operation.

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?

Three short lines, no filler, with the resource statement front-loaded and the error constraint immediately after the parameter it applies to. Slightly telegraphic rather than fully structured, but nothing is wasted.

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?

With an output schema present, return values need not be explained. For a 2-parameter read operation the description covers both parameters and one failure mode, which is close to sufficient; only pagination/size guidance is arguably missing.

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 carries the burden and largely meets it: it explains that workspace_id is numeric-only (with the failure mode) and that workspace is a customer slug that may be omitted when only one workspace exists. Format of the slug and whether workspace_id resolves account/container are not stated.

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 the resource precisely: user-defined variables within a workspace, which is distinct from sibling tools like gtm_list_tags, gtm_list_triggers, or gtm_list_workspaces. It omits an explicit verb, relying on the name's 'list', but the object and scope are unambiguous.

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?

Only conditional guidance given is that 'workspace' is optional when there is a single workspace. No statement of when to use this versus gtm_list_tags/gtm_list_triggers or what prerequisites (account/container resolution) must precede the call.

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