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

Annotations already cover read-only, idempotent, and non-destructive behavior. The description adds the authentication requirement and clarifies that the count is scoped to the authenticated user's own instances, which is useful operational context beyond what the annotations provide.

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?

A single sentence that front-loads the action and resource, followed by the key authentication requirement. No wasted words or redundant restatements of the tool name.

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 count operation with an optional parameter and strong annotation coverage, the description is largely complete. It states the essential authentication requirement and ownership scope; the return value is self-explanatory as a count, so no output schema is necessary.

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 single optional sessionKey parameter is fully documented in the schema (100% coverage), so the baseline of 3 applies. The description does not add any parameter-specific semantics, but it does hint that authentication is required, which is indirectly related to the sessionKey.

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 the verb 'Get' and the resource 'total count of VPS instances', scoped to the authenticated user. This clearly distinguishes it from sibling tools like listMyVpsInstances, which returns a list, and getVpsInstanceDetails, which returns details for one instance.

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 implies usage for counting instances rather than listing them, but it never explicitly names alternatives or says when to choose this tool over listMyVpsInstances. The authentication requirement is stated, but no when-to-use or when-not-to-use guidance is provided.

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