aws_list_ec2_instances

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

No annotations are provided, so the description carries the full burden. It implies a read-only listing but says nothing about pagination, whether instances across all states are returned, permission requirements, or error behavior for invalid credentials. For a zero-annotation tool this is a thin behavioral profile.

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 purpose is front-loaded in a single sentence, followed by a compact Args block that maps directly to the parameters. No filler text, though the Args/Sphinx style is slightly verbose for only two parameters.

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?

An output schema exists, so return values need not be explained, and with 2 optional parameters complexity is low. However, with no annotations and no mention of credential prerequisites or result scope (all instances vs. running only), the description is adequate but leaves meaningful gaps for an agent invoking it cold.

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 0%, so the description must compensate, and it does: it names both parameters, gives concrete region examples ('us-east-1', 'us-west-2'), and restates the profile default. It does not discuss region format validity beyond examples or profile resolution rules, but the added value over the bare schema is substantial.

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 and resource ('List EC2 instances') plus the scoping dimensions (region, profile). The resource is distinct from all siblings (EKS clusters, profiles, caller identity), so an agent can route by resource without opening the schema. It stops short of explicitly naming an alternative tool, which keeps it at 4.

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?

There is no guidance on when to use this versus the sibling listing tools, nor on prerequisites such as whether credentials for the named profile must already exist. The description only says a profile is 'used', leaving context entirely to inference.

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