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

Annotations already cover the safety profile (mutating, non-idempotent, non-destructive, closed-world), and the description adds genuinely new context: the variable is created STAGED in a specific managed workspace and will never be published. That staging semantics is exactly the kind of trait annotations cannot express. It still omits permission requirements and what happens if a same-named variable exists.

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 tight and front-loaded with the scoping distinction. The 'Tools revision: 5c9bea8f' trailer is internal metadata that does nothing for an agent selecting or invoking the tool.

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. But for a 4-parameter mutation tool with zero schema documentation, the description says nothing about the type enum space, the container identifier format, or the shape of the parameter array — the core input an agent must construct.

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 all four parameters, so the description carries the full burden and largely fails: name, container path format, and the GTM variable 'type' taxonomy are undocumented. The parameter array (the actual variable configuration payload) is not mentioned at all, leaving an opaque untyped item collection.

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 ('Create a user-defined variable') and scopes it to a staged, never-published state. 'User-defined' implicitly distinguishes it from gtm_enable_built_in_variable, though no sibling is named directly.

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?

No guidance on when to use this versus gtm_update_variable or gtm_enable_built_in_variable, and no prerequisites stated (workspace selection, container requirement). The 'never published' note hints at a staging workflow but does not tell the agent what to do next or when this is the right call.

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