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

With no annotations, the description carries the full behavioral burden. It usefully discloses a real constraint beyond the schema: free for non-commercial use with attribution, commercial use requires Pro. However, it says nothing about authentication, rate limits, read-only nature, or what happens with an invalid id, so the transparency is partial.

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 front-loaded sentence that leads with the core action before listing returned fields. It is dense but every clause names a distinct output artifact; the trailing licensing sentence is justifiably separate.

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?

There is no output schema, so the description must describe returns, and it does so thoroughly (prices at three usage tiers, term, fees/credits text, parsed bill credit, EFL link, monthly and annual estimates). The main gap is operational detail: valid id format, error behavior, and when to prefer sibling tools.

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 67%: kwh and months are documented in the schema, while id is a bare integer. The description adds some value by linking usage to output ('estimated monthly bill at several usage levels and the annual estimate for the given usage'), clarifying what kwh/months drive, but it adds no format or constraint detail beyond the schema descriptions.

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+resource combo ('One plan by id') and enumerates the plan attributes returned, so an agent immediately understands this is a single-plan lookup. It implicitly separates itself from list-oriented siblings like electricity_cheapest or electricity_rank_plans, but never names them, so the differentiation is inferred rather than stated.

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 is only implied: you fetch a single plan when you already have its id. There is no explicit guidance on when to reach for this versus electricity_cheapest, electricity_rank_plans, or electricity_compare_my_plan, nor any statement about how to obtain a valid id. The licensing note (free non-commercial, Pro for commercial) is the only explicit usage constraint, and it concerns compliance rather than tool selection.

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