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

Annotations only declare readOnlyHint=true; the description adds the material behavioral fact that the underlying data is state-level from EIA Form 861, so ZIP-level precision should not be assumed. That granularity caveat is exactly the kind of context an agent needs, though it says nothing about freshness lag or coverage gaps for non-US ZIPs.

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 tight sentences, front-loaded with the resource and units, then the caveat and sibling routing. No filler and nothing repeated from the schema.

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 carries the return-value burden and does so: it specifies units ($/kWh and cents/kWh), the sector dimension, the monthly averaging period, and the geographic granularity. Nothing needed to call or interpret the tool 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?

Only one parameter, and schema description coverage is 100% (the ZIP pattern and format are fully documented in the schema). The description adds no parameter-level meaning beyond the schema, 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 the latest monthly average retail electricity rate) plus units, geography, and the sector breakout. It also names the sibling it is not (utility_tariff), so an agent can distinguish it without opening schemas.

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?

Explicitly frames the when-not case ('a ballpark, not utility- or ZIP-specific tariffs') and routes to the correct alternative by name ('use utility_tariff for those'). The condition selecting each tool is unambiguous.

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