AWS MCP Server

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

Annotations already declare readOnlyHint=true, destructiveHint=false, openWorldHint=true, and idempotentHint=true, covering safety and idempotency. The description adds minimal behavioral context beyond this—it implies regional scoping but doesn't mention pagination behavior (implied by NextToken parameter), rate limits, or authentication requirements. With annotations doing heavy lifting, the description adds some value but not rich behavioral disclosure.

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 a single, efficient sentence with zero wasted words. It's front-loaded with the core action and resource, making it easy to parse quickly. Every word earns its place without redundancy.

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 (2 parameters with nested objects, no output schema), the description is minimal. Annotations provide safety and idempotency info, but the description lacks details on return values, error handling, or usage context. It's adequate for a basic list tool but leaves gaps in guiding the agent on full functionality.

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 50%, with parameters like region and VpcArgs documented in the schema. The description mentions 'given region' but doesn't add details beyond what the schema provides for region or explain the complex VpcArgs object (which includes filtering, pagination, etc.). It compensates slightly but doesn't fully address the coverage gap, meeting the baseline for moderate schema coverage.

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 verb ('List') and resource ('all the VPCs') with regional scope ('in the given region'), making the purpose specific and understandable. However, it doesn't explicitly differentiate from sibling list tools like list-subnets or list-route-tables, which would require mentioning it's specifically for VPCs rather than other AWS resources.

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 no guidance on when to use this tool versus alternatives. It doesn't mention prerequisites, when not to use it, or how it differs from other list tools in the sibling set. The agent must infer usage from the tool name alone.

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