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

The annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, covering the safety profile. The description adds detail about the response fields (e.g., kind, type, mode) which is useful context beyond the annotations. However, it does not disclose any additional behavioral traits such as pagination, rate limits, or authentication requirements. No contradiction exists. With annotations present, the description provides moderate added value.

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 informative but somewhat verbose. It front-loads the main purpose and then lists many response fields, which is useful. However, the closing sentence 'Requires project, zone, and instance name as input.' is redundant given the schema's required fields and could be trimmed. Overall, it is structured in a single sentence but includes a lengthy enumeration that could be more concise.

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?

For a read-only list tool with an output schema available, the description is fairly complete. It clearly states the operation, the required inputs, and the nature of the response (listing attached disks with many fields). It does not mention pagination or filtering, but the presence of an output schema likely covers return structure. Given the tool's simplicity and annotation support, no critical information is 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?

The input schema has 100% description coverage for all three required parameters (project, zone, name). The description only restates that these are required, without adding meaning beyond what the schema already provides. Since the schema fully documents each parameter, a baseline of 3 is appropriate.

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 specific verb 'Lists' and the resource 'disks attached to a Compute Engine virtual machine (VM) instance'. It distinguishes itself from sibling tools like list_disks and list_instances by focusing on attached disks of a specific instance, making the purpose 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?

The description does not provide explicit guidance on when to use this tool versus alternatives. It only states what it does and mentions required inputs. No exclusions or routing to sibling tools like list_disks or get_instance_basic_info are given, leaving the agent to infer the appropriate context.

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