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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), and the description adds substantial behavior beyond them: the provenance of the lookup tables (Loughborough half-hourly monitoring, modelled battery), the three indexing inputs, the documented defaults (3,500 kWh consumption, 'in_half_the_day' occupancy), the fact that supplying prices adds a pound value to the result, and that both self-consumption and grid independence are reported.

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?

The purpose is front-loaded in the first sentence and the structure moves cleanly from what it does, to the data source, to the inputs, to caveats. It is a little long, with the monitoring-data flavor paragraph and the MCS/installer boilerplate doing less work than the parameter guidance, but nothing is confusing or misplaced.

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 return values need not be described, and the description still tells the agent everything else it needs: defaults for omitted inputs, the units and meaning of battery capacity, the effect of supplying prices, and the distinction between the two reported metrics. For a six-parameter calculator this is complete.

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, but the prose adds genuine meaning: it explains why battery capacity must be usable (smaller than the headline figure), why generation should come from MIS 3002, and why consumption should come from a metered bill. It largely reinforces rather than extends the schema text, so it stops short of a 5.

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 opens with a specific verb and resource: estimating the proportion of a domestic PV system's annual output that is self-consumed versus exported. It even pre-empts a likely confusion by stating that self-consumption is not grid independence, which separates it from solar_pv_output (generation) and solar_pv_system_size (sizing) without needing to name them.

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?

Usage context is implied rather than stated: the closing lines say these calculators are 'for understanding a system and checking a quotation.' There is no explicit when-to-use versus solar_pv_output or solar_pv_shading, no stated prerequisites (e.g. run solar_pv_output first), and no exclusions. The agent must infer the routing.

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