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

With no annotations, the description carries the full burden and does so well: it explains that data is kept, that convert adds a public IP, that convert_to_nat drops the IP and refunds the unused difference, that shrink is impossible for vCPU/RAM/disk, and that the server must be active. It also previews the returned fields and what prorated_topup means.

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?

Dense but front-loaded, with the core purpose first and the modes/output/constraints following. Heavy parenthetical use makes it a single run-on paragraph rather than scannable structure, but every sentence carries useful information.

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?

Without an output schema, the description still lists the returned fields (product_id, name, monthly, prorated_topup, mode) and explains the prorated charge semantics. Constraints and preconditions are all present, so an agent has everything needed to call and interpret this tool.

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?

Only one parameter exists and schema description coverage is 100%, so the schema already documents service_id thoroughly. The description adds no syntax or format detail beyond the 'server must be active' precondition, making the baseline 3 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?

States a specific verb ('List') and a precise resource ('the plans this VPS can switch to IN PLACE with its data kept'), and names the three switch modes (resize, convert, convert_to_nat) that define the scope. This distinguishes it from list_plans (all plans) and change_plan (performs the switch) without needing their schemas.

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?

Clearly says when the tool applies: the server must be active, options are in-place with data retained, and shrinking is explicitly not possible. It does not name change_plan as the follow-up action nor state alternative tools for other cases, but the context is unambiguous.

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