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

With no annotations provided, the description carries the full burden of behavioral disclosure. It discloses the authentication requirement and implies a read-only aggregate operation via 'total count', which is meaningful context. However, it does not explicitly state that the operation is side-effect-free, what happens with zero instances, or the exact response format.

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?

Two short sentences with zero wasted words. The core purpose is front-loaded in the first sentence, and the authentication requirement is a valuable clarifying second sentence. Every word earns its place.

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 tool with one optional parameter and no output schema, the description is largely complete: purpose, scope, and auth requirement are all covered. The main gap is that no output schema exists and the description does not clarify the exact return shape (e.g., a bare integer vs. an object with a count field), though 'total count' strongly implies a numeric return.

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%, and the schema already fully documents the sessionKey parameter, including its format, origin, and when to include or omit it. The description adds no parameter-level information, so the baseline of 3 applies since the schema does the heavy lifting.

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 uses a specific verb ('Get') and a specific resource ('total count of VPS instances') with a clear scope ('owned by the authenticated user'). It clearly states an aggregate/count operation rather than a listing operation, which implicitly distinguishes it from listMyVpsInstances, but it does not explicitly name or differentiate any sibling.

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 states a precondition ('Requires authentication') but provides no guidance on when to use this tool versus alternatives such as listMyVpsInstances or getVpsInstanceDetails. There are no exclusions, no when-to-use conditions, and no mention of scenarios where the count tool is preferable over listing instances.

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