get_vsan_capacity

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

Annotations cover the safety profile (readOnly, idempotent, non-destructive), and the description adds substantial beyond-annotation behavior: null vs 0 for inaccessible datastores with the explicit rationale that vCenter returns 0 and '0 GB used reads as a healthy empty datastore', accessible=null meaning the summary was silent, and vsan_enabled=false rather than an error. This is exactly the kind of guidance an agent cannot infer from structured fields.

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?

Front-loaded with the read tag and purpose, then the return shape, then the non-obvious failure semantics, then sibling routing. Every sentence carries information; the only near-redundancy is the trailing 'No side effects.'

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?

There is no output schema, so the description carries the return contract itself by enumerating the fields and the three accessible states. Combined with the stated error condition and sibling alternatives, nothing an agent needs to call this correctly is missing.

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 both parameters are documented in the schema, including the 'errors if the cluster is not found' note that the description repeats. The description adds no new parameter-level syntax or format detail, so the baseline 3 applies.

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 and resource ('Get space usage of a cluster's vSAN datastore for capacity planning') with the exact scope named. It clearly separates itself from get_vsan_health and list_all_datastores by naming both and their domains.

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?

Explicit routing: 'Use get_vsan_health for disk-group layout and host details; use list_all_datastores for non-vSAN (VMFS/NFS) datastore usage.' It also states the one error condition (cluster name not found), so an agent knows the boundary of valid use.

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