update_alias

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

With no annotations provided, the description carries the behavioral burden. It clearly discloses that this mutates an alias-to-key association and explains the intended effect: application code referencing the alias picks up the new key automatically. It does not cover failure modes or permissions, but the core side effect is 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?

The description is short and front-loaded, but the second sentence repeats much of the first: 'Point an alias to a different key...' essentially restates 'point the existing alias to the new key ARN...'. The core message could be delivered in one sentence plus the parameter details.

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 mutation with no output schema, the description is nearly complete: it covers purpose, when to use it, both parameters, and the expected behavioral effect. Minor gaps such as what happens if the alias does not exist or what the API returns are not stated, but the tool's simplicity mitigates their impact.

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?

The schema provides only property titles and no descriptions (0% coverage), so the description must compensate. It documents both parameters in the Args section, including the critical 'alias/' prefix requirement for alias_name and the semantic role of key_arn as the new target key. This fully compensates for the schema's lack of detail.

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 opens with a specific use case ('when rotating a key') and a precise action: repoint an existing alias to a new key ARN. This clearly communicates the tool's resource and behavior, and distinguishes it from create_alias or delete_alias.

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?

It explicitly states when to call the tool—during key rotation—and explains the benefit of keeping application code unchanged. It does not explicitly name alternatives or exclusions, but the 'existing alias' vs. new alias framing makes the boundary with create_alias reasonably clear.

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