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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered structurally. The description adds the useful caveat that results are planning estimates rather than code/wiring approval, but says nothing about precision, rounding, or what the returned kW figure represents.

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?

Four short sentences, front-loaded with the computation and then the unit convention and disclaimer. Every sentence contributes, though "Ask for actual measurements" is a directive that sits slightly awkwardly among descriptive content.

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 no output schema, the description does state the output unit (kW) and the planning-estimate framing, which is enough to call the tool. It stops short of describing the shape of the result or any recommendation it may return, but nothing needed to invoke it 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 coverage is 0%, yet the description names essentially every input: room dimensions, glass area, wall insulation and supply voltage. It also adds meaning the schema cannot express — unit values map to meters/square meters versus feet/square feet — which is exactly the compensation needed at zero coverage. Minor gap: it doesn't explain the insulated vs uninsulatedOrLog distinction or the 208/240 V choice.

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 ("Estimate electric heater kW") plus the exact inputs it derives from, which immediately separates it from the sibling quote/cost/brand tools. An agent knows from the first sentence what this tool computes.

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?

Gives clear usage context ("Ask for actual measurements") and an explicit exclusion: it is a planning estimate, not approval of wiring, clearances or a particular heater. It does not name the sibling it hands off to for quoting or costing, so routing is implied rather than spelled out.

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