aws_run_instances

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

With no annotations, the description carries full burden. It discloses 'Costs money — billing starts immediately' and 'Reserved for dangerous guard mode,' adding crucial behavioral context beyond the schema. It does not mention permissions or error handling, but is otherwise transparent.

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?

Four sentences, each earning its place: action, cost/danger, usage restriction, user confirmation instruction, return format. Front-loaded and no fluff.

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 high complexity of launching EC2 instances, the description covers cost, danger, user confirmation, and return format. Lacks mention of error handling or IAM permissions, but is fairly complete for a dangerous tool. Schema covers all parameters well.

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%, so baseline is 3. The description references parameters to summarize (AMI, instance type, region, count) but adds no new semantics beyond what the schema already provides.

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 'Launch one or more new AWS EC2 instances,' providing a specific verb and resource. It distinguishes from siblings like aws_start_instance and aws_terminate_instance, which handle different lifecycle states.

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 instructs to 'Summarise AMI, instance type, region, count, and confirm with the user before calling,' and states 'Reserved for dangerous guard mode,' giving clear usage context. It does not explicitly mention alternatives, but the user confirmation directive is strong.

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