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

Annotations already declare readOnlyHint=true, idempotentHint=true, destructiveHint=false, and openWorldHint=false, so safety and determinism are covered structurally. The description's added value is the note that it reproduces a published calculator's logic, implying consistent deterministic output, but it discloses nothing about I/O behavior or edge cases beyond that. With the lower bar set by annotations, a 3 is appropriate.

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 sentences, front-loaded with the core capability before the reference link. The external URL is arguably promotional rather than operational, but it is brief and does signal provenance/determinism, so it roughly 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 six-parameter calculator with zero schema descriptions and no output schema, the description should explain the input-output relationship (e.g. batteryAh + loadWatts yields runtime; targetHours yields required capacity). It does not, leaving the agent unable to reason about which optional parameters to supply for which requested answer.

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 0% across six parameters, so the description carries the burden and largely fails to. It mentions concepts that loosely map to loadWatts, batteryAh, and targetHours, but gives no units, defaults, ranges, or explanation of how batteryType/inverterEfficiencyPercent affect results. An agent cannot tell which input drives which of the three advertised outputs.

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 ("Estimate") and enumerates three concrete outputs: runtime, required battery capacity, and minimum UPS rating. That is far clearer than a tautology and tells an agent this is a pure calculation tool. It does not explicitly differentiate itself from the sibling calculate_cctv_storage, but the domains are distinct enough that confusion is unlikely.

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?

Usage is only implied via the parenthetical example "(e.g. during load-shedding)," which gives a real scenario but no explicit when-to-use/when-not and no named alternatives. An agent can infer this is the tool for UPS/battery sizing, but nothing steers it away from siblings or states prerequisites.

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