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

Annotations only declare readOnlyHint=true, so the description carries the behavioral load and does it well: it discloses staleness (data lags up to a day, not real-time), what the response contains (per-hour fuel mix, total generation, carbon intensity), and the methodology caveat (fixed per-fuel combustion factors on in-BA generation, no imports, so values won't match eGRID annual factors). These are exactly the traits an agent needs to avoid misusing the output.

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?

Three sentences, zero filler, and front-loaded: the core capability and scope come first, followed by latency, output shape, and the fit/exclusion guidance. Every sentence carries distinct decision-relevant information.

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?

No output schema exists, yet the description states the return shape (time series with per-hour fuel mix, total generation, carbon intensity). Combined with latency, methodology, and alternative routing, an agent has everything needed to select and call this correctly.

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 100%, so the baseline is 3 and the schema already documents ba/zip/hours/aggregate. The description adds genuine meaning on top: it clarifies aggregate's semantics (24-hour average profile over the trailing 168 hours), warns that buckets are UTC, and redirects local-time windows to cleanest_hours. It adds little on hours/ba/zip, keeping it just above baseline.

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+resource+scope: hourly grid carbon intensity (kg CO2e/kWh) for any US ZIP code, derived from EIA-930 fuel-mix data. It also names the specific alternative tools (cleanest_hours, WattTime, Electricity Maps) and the data source, so an agent can distinguish it from siblings like calculate_emissions or lookup_emission_factor 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?

Gives explicit when-to-use (demand response, load shifting, grid pattern timing/analysis) and when-not (inventory reporting, because methodology differs from eGRID). It routes the agent to alternatives for live/forecast data (WattTime, Electricity Maps) and to cleanest_hours for local-time scheduling windows. This is as complete as usage guidance gets.

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