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

Annotations already establish readOnlyHint=true and openWorldHint=false, so safety is covered. The description goes further by disclosing data provenance and method (DESNZ/MCS cost records, PVGIS reference-city generation, simple payback at the DESNZ small-business price), which tells the agent how the numbers are constructed and that they are modelled rather than live-queried.

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?

A single sentence with no filler; the three returned metrics are front-loaded and the qualifiers (size band, geography) trail them. It is dense enough that the parenthetical sources interrupt the read slightly, but nothing is redundant.

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 correctly enumerates the three return values, and the annotations cover the safety profile. Minor gaps remain – units for payback (years) and generation (kWh) are not stated – but an agent has enough to call the tool and interpret the response.

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% and the schema documents the default kW=30 and the region format, but the description adds the validity range (10-50 kW) for kw and clarifies that region means a Great Britain region – information not present in the schema. That is meaningful added meaning over structured fields.

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 names the exact resource it returns – average cost per kW, yearly generation, and simple payback – plus the size band (10-50 kW) and geography (Great Britain region). It is precise enough that an agent can tell it computes solar economics rather than charging economics, though it never explicitly names or rules out the closest siblings (charging_cost, business_electricity_prices).

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?

There is no when-to-use or when-not-to-use statement and no alternative tool is named, even though siblings like charging_cost and business_electricity_prices overlap in domain. The only implicit scoping is the 10-50 kW / Great Britain range, so the agent must infer the use case from the metrics listed.

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