Google Compute Engine

list_instances

Read-onlyIdempotent

Lists Compute Engine virtual machine (VM) instances. Details for each instance include name, ID, status, machine type, creation timestamp, and attached guest accelerators. Use other tools to get more details about each instance. Requires project and zone as input.

Input Schema

TableJSON Schema

Name	Required	Description
`zone`	Yes	Required. The zone of the instances.
`project`	Yes	Required. Project ID for this request.
`pageSize`	No	Optional. The maximum number of instances to return.
`pageToken`	No	Optional. A page token received from a previous call to list instances.

Output Schema

TableJSON Schema

Name	Required	Description	Default
`instances`	No	The list of instances.
`nextPageToken`	No	A token that can be sent as `page_token` to retrieve the next page. If this field is omitted, there are no subsequent pages.

TDQS

A4/5.0

Behavior3/5

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

Annotations already declare readOnlyHint=true, idempotentHint=true, and destructiveHint=false, so the safety profile is fully covered. The description adds the returned fields and notes the requirement for project and zone, but these are largely redundant with the schema. It hints at the tool's limited scope without explicit behavioral nuance.

Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.

Conciseness5/5

Is the description appropriately sized, front-loaded, and free of redundancy?

The description is three sentences, front-loaded with the core purpose, and every sentence provides value: what the tool does, what fields are returned, and how to use it. There is no fluff or repetitive text.

Shorter descriptions cost fewer tokens and are easier for agents to parse. Every sentence should earn its place.

Completeness4/5

Given the tool's complexity, does the description cover enough for an agent to succeed on first attempt?

Given the output schema and strong annotations, the description covers the essential purpose, returned fields, and required inputs. It does not explicitly differentiate from list_managed_instances or mention pagination, but those are largely addressed by the schema and tool naming. A minor gap exists in not clarifying zone-scoped listing beyond the required parameter.

Complex tools with many parameters or behaviors need more documentation. Simple tools need less. This dimension scales expectations accordingly.

Parameters3/5

Does the description clarify parameter syntax, constraints, interactions, or defaults beyond what the schema provides?

Schema coverage is 100% with descriptive entries for all four parameters. The description only restates that project and zone are required, adding no new meaning beyond what the schema already provides. Baseline 3 is appropriate given the high schema coverage.

Input schemas describe structure but not intent. Descriptions should explain non-obvious parameter relationships and valid value ranges.

Purpose5/5

Does the description clearly state what the tool does and how it differs from similar tools?

The description clearly states 'Lists Compute Engine virtual machine (VM) instances' and enumerates the exact fields returned, which distinguishes it from sibling list tools for disks, images, machine types, etc. The verb-resource pairing is immediate and unambiguous.

Agents choose between tools based on descriptions. A clear purpose with a specific verb and resource helps agents select the right tool.

Usage Guidelines4/5

Does the description explain when to use this tool, when not to, or what alternatives exist?

'Use other tools to get more details about each instance' explicitly signals that this tool provides basic info and is not for deep investigation. However, it does not name specific alternative tools like get_instance_basic_info or list_managed_instances, so the guidance is useful but not exhaustive.

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

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TDQS

A3.6/5.0

Disambiguation5/5

Each tool targets a distinct resource-action combination. For resources with both basic and detailed getters (reservations, templates), the suffixes clearly differentiate them, and list vs get distinctions are unambiguous. No two tools appear to do the same thing.

Naming Consistency5/5

All tool names follow a consistent verb_noun pattern with snake_case (e.g., create_instance, list_disks, get_zone_operation). Getters consistently use descriptive suffixes like basic_info, details, or properties. No mixed naming conventions or vague verbs.

Tool Count4/5

29 tools is slightly above the ideal range but justified given the breadth of Google Compute Engine resources covered (instances, disks, templates, reservations, commitments, MIGs, snapshots, images, machine types, accelerator types). Each tool serves a specific purpose and contributes to the overall scope.

Completeness2/5

The toolset is heavily read-oriented. While instances have full lifecycle coverage (create, delete, start, stop, reset, set machine type), most other resources lack write operations: disks, templates, reservations, commitments, snapshots, and MIGs only have get/list tools. This creates dead ends for agents needing to create or modify these resources, which is a significant gap for a GCE management server.

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