Per-disk capacity, health and free bays

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

Annotations already declare readOnlyHint=true and openWorldHint=true, and the description's 'Read-only' line merely restates that. The valuable additions are the ZDR-pool caveat explaining why disk-level data can contradict pool-level free space, and the power_on_hours interpretation tip about previously used drives, neither of which is derivable from annotations or schema.

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 purpose is front-loaded and the usage guidance follows logically, but the explicit return-shape listing duplicates the output schema that already exists, which is wasted text. The illustrative 476 GiB / 59.8 GiB example is helpful but adds length.

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?

With readOnly/openWorld annotations and a full output schema present, the description needs only to justify when to call the tool and what pitfalls exist. It does both, including the disk-vs-pool free-space trap and sibling routing, so nothing an agent needs 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?

The tool takes zero parameters, so the baseline is 4 and there is nothing for the description to disambiguate. The documented return fields do not function as parameters here.

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 opening sentence names a specific verb ('Report') and resource ('every physical disk') and enumerates exactly what is covered: free space, temperature, health, SMART counters, fragmentation, power-on hours, and empty bay counts. It is clearly separable from siblings like zspace_smart and zspace_usage, which it explicitly names later.

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?

It gives an explicit trigger ('Use before recommending a drive purchase or when a pool is nearly full') and explains why the tool is needed over the pool-level alternative, with a concrete observed example of a misleading pool report. It also routes the agent to zspace_smart for full SMART attributes and zspace_usage for pool totals.

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