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

Annotations already show the operation is not read-only and not destructive. The description adds useful behavioral details like 'miễn phí' and 'SSL tự động', but it does not disclose side effects such as DNS propagation, whether attaching is idempotent, or what happens on duplicate labels.

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 sentence with no unnecessary filler. It front-loads the core action and includes the key benefits (free, automatic SSL) 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?

For a simple two-parameter mutation tool with 100% schema coverage and no output schema, the description is mostly complete: it states the target VPS condition, the domain format, and value-add behavior. It leaves out return/error behavior, but that is a minor gap for such a straightforward operation.

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 the schema already explains both parameters. The description's reference to '<tên>.tocbien.app' reinforces the label pattern but does not add meaning beyond what the schema provides, so the baseline score of 3 is appropriate.

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 states a specific verb ('Gắn' / attach), a clear resource ('subdomain <tên>.tocbien.app'), and the target object ('một VPS đang chạy'). This clearly distinguishes it from the sibling tools, none of which handle subdomains.

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 gives clear context for when the tool applies: to a running VPS. It does not explicitly list alternatives or exclusions, but the sibling set contains no competing subdomain tool, so the intended use is reasonably clear.

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