List VPC subnets in a given AWS region to discover subnet IDs for EC2 launches. Pass those IDs to aws_run_instances.
List VPC subnets in the given region. Use the subnet_id values as the subnet_id argument to aws_run_instances.
| Name | Required | Description | Default |
|---|---|---|---|
| region | Yes | AWS region (e.g. us-east-1). | |
| account | No | AWS account label to act in; omit for the default account. |
Changes observed during successful MCP inspections.
v2.28.0Input schema / properties / accountAdded value: +{
+ "description": "AWS account label to act in; omit for the default account.",
+ "type": "string"
+}v2.24.0v2.23.8v1.0.0Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
No annotations are provided, so the description carries the full behavioral burden. "List" does imply a safe, non-destructive read, and the chaining hint tells the agent what the output contains, but there is no mention of permissions, pagination, or throttling behavior for a multi-result AWS listing call.
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?
Two short sentences, zero filler. The purpose is front-loaded and the second sentence is a distinct, actionable workflow instruction rather than padding.
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 simple two-parameter list tool with no output schema, the description covers purpose, scope, and the handoff to aws_run_instances. It does not state the return shape or ordering, though the chaining hint implicitly reveals that subnet_id values are present in the output.
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% for both parameters, so the schema already documents region and account. The description restates region's role but adds no meaning beyond what the schema provides, and never mentions the account parameter.
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 (List) and resource (VPC subnets) scoped to a region. The resource is unambiguously distinct from sibling aws_list_* tools (amis, regions, key pairs, security groups), so an agent can select it without opening the schema.
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?
Adds concrete downstream routing: use the returned subnet_id values as the subnet_id argument to aws_run_instances. That is genuine when-to-use guidance, but there is no when-not or mention of the other subnet-consuming alternatives.
Agents often have multiple tools that could apply. Explicit usage guidance like "use X instead of Y when Z" prevents misuse.