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

Annotations already declare readOnlyHint and openWorldHint, and the description adds real context beyond them: the NSRDB typical-year weather source, the caveat that this is an estimate rather than a yield guarantee, and the pricing model ($0.002 USDC per successful call via x402 on Base/Solana/Arc, with failed calls free). It stops short of latency, rate limits, or quota behavior, so it is strong but not exhaustive.

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?

Front-loaded with the core capability and outputs before the caveat, sibling pointer, and pricing, and each sentence carries distinct information. Minor deductions for the awkward 'Related tools on this server, for a different need:' lead-in and the incomplete trailing phrase 'at one.'

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?

An output schema exists, so explicit return-value enumeration is supplementary rather than required here. The description covers data source, accuracy caveat, sibling alternative, and cost, which is nearly everything an agent needs for a paid, read-only simulation call; only operational details like latency or failure modes are absent.

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 100% and every parameter (lat, lon, tilt, azimuth, capacityKw) is documented with ranges and defaults in the schema itself. The description only loosely implies the lat/lon and system input by describing the tool as an estimate 'at a latitude and longitude,' adding no format, unit, or default guidance beyond what structured data already provides. Baseline 3 is appropriate.

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 pair (PVWatts v8 estimate for a grid-connected PV system at a lat/lon) and enumerates the concrete outputs: annual AC energy, capacity factor, annual solar radiation, monthly AC energy. It also explicitly distinguishes itself from the nearest sibling, energy_global_solar_atlas_pv, so an agent can choose without opening either schema.

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 routes the agent to energy_global_solar_atlas_pv 'when you need Global Solar Atlas long-term average solar resource,' which implicitly frames this tool as the site-specific production simulation. That said, the when-to-use framing is one-directional and the alternative sentence ends in a truncated fragment ('at one.'), so the exclusion guidance is clear but slightly incomplete.

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