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 mentions regional filtering but doesn't address pagination (implied by NextToken/MaxResults in schema), rate limits, or authentication needs. No contradiction with annotations exists.

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 front-loads the core action ('List EC2 instances') and includes essential scope ('in a given region'). Every word earns its place, making it easy for an agent to parse quickly.

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 moderate complexity (2 parameters with nested objects), rich annotations, and no output schema, the description is minimally adequate. It covers the basic purpose but lacks details on pagination, error handling, or output format, which would help the agent use it correctly. The annotations provide safety context, but the description could add more operational guidance.

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 'Ec2Args.Filters' well-documented in the schema. The description only mentions 'region' and implies filtering but adds no details on parameter usage, syntax, or examples. It doesn't compensate for the coverage gap, so the baseline 3 is appropriate given the schema does partial work.

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 ('EC2 instances') with regional scope ('in a given region'). It distinguishes from siblings like 'list-amis' or 'list-security-groups' by specifying EC2 instances. However, it doesn't explicitly differentiate from 'launch-ec2-instance' or other EC2-related tools beyond the obvious list vs. create distinction.

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 sibling tools like 'list-amis' or 'list-instance-tags' for related queries, nor does it specify prerequisites (e.g., AWS credentials) or typical use cases. 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.