variables_update

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

With no annotations provided, the description carries full responsibility for behavioral disclosure. It only indicates '[WRITE]' and prerequisites, but omits details on error handling, idempotency, permissions, or side effects. For a mutation tool, this is insufficient.

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 very short (one line) and front-loaded with the action and prerequisites. Every word serves a purpose, but the extreme brevity limits completeness. It is concise without being unnecessarily verbose.

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?

Given the tool's complexity (10 parameters, write operation, no annotations, no output schema), the description is severely lacking. It fails to explain parameter semantics, return values, or error conditions, making it insufficient for effective use.

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?

The schema has 10 parameters with 0% description coverage, and the tool description adds no explanation for any parameter. Key parameters like 'fingerprint' and 'parameter' are left entirely to the agent's inference, making it difficult to use correctly.

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 clearly states the action ('Update a GTM variable') and includes a '[WRITE]' tag. It is specific about the resource and verb, though it does not explicitly differentiate from sibling tools like variables_create or tags_update. The name and description together make the purpose evident.

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 description provides critical usage prerequisites (GTM_MCP_ENABLE_WRITES=true and confirm=true), which help the agent know when the tool is available. However, it does not offer guidance on when to use this tool versus alternatives like tags_update or variables_create, nor does it specify conditions that would make it inappropriate.

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