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

The annotations already declare destructiveHint=true and readOnlyHint=false, so the mutation safety profile is known. The description adds useful behavioral context by instructing to check for errors and the operation status being DONE, and directing to get_zone_operation for details. This goes beyond the annotations but does not deeply describe side effects or permissions.

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 three concise sentences with no unnecessary fluff. The first sentence states the purpose, the second lists required inputs, and the third provides operational guidance. While the input requirement sentence slightly duplicates the schema, it is brief and does not detract from the overall clarity.

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 that this is a straightforward start operation with an output schema present, the description adequately covers the invocation flow: call the tool, check for errors and DONE status, and use get_zone_operation for details. It does not explain what happens to the instance (e.g., transitions to RUNNING), but that is not essential for this tool's 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?

Schema description coverage is 100%, so the baseline is 3. The description merely states that project, zone, and instance name are required, which restates the schema without adding any new meaning or parameter-level detail. No extra context is provided for these parameters.

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: 'Starts a Google Compute Engine virtual machine (VM) instance.' This specific verb+resource combination distinguishes it from sibling tools like create_instance, delete_instance, stop_instance, and reset_instance. It also notes the required inputs, further clarifying the intended operation.

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 implies the tool is for starting an existing stopped VM but does not explicitly state when to use it versus alternatives like reset_instance. It provides guidance on proceeding only after verifying the operation status is DONE, which is more about post-invocation handling than usage context. No explicit exclusions or alternative-tool references are given.

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