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

Annotations already declare readOnlyHint=true and openWorldHint=false, so the safety profile is covered. The description adds genuinely useful behavior beyond that: the rate vintage (October 2026 announcement), the fact that lifeline discounts and local taxes are excluded, and that the response includes source and page URL — all consistent with a read-only, closed-world lookup.

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?

Purpose is front-loaded and the whole thing is short, but it is a run-on with redundant fragments ('Same code as <url>. Reference: Source: ...') that repeat rather than add information. Trimming the URL and the duplicated 'Reference/Source' would lose nothing.

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?

For a single-parameter, no-output-schema calculator, the description covers what the agent needs: what is computed, what is excluded, what the return contains, and the data vintage. Only the meaning/units of 'kwh' and the applicable region boundary are left implicit.

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?

There is only one parameter and schema description coverage is 0%, so the schema documents only type/default/min/max. The description never mentions 'kwh' at all, though the unit is self-evident from the name and the electricity-bill domain, so an agent can still call it correctly.

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 states the resource (Philippines Meralco residential bill for the current month) and implies the action (estimate a bill from usage), which distinguishes it from the regional siblings like jp_electricity and kr_electricity. However, the verb is never explicit ('calculates/estimates'), so the agent must infer it from the name and the kwh parameter.

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?

Scope is implied by the title/region, and the exclusion note (lifeline discounts and local taxes not included) tells the agent when the result is not applicable. But there is no explicit when-to-use guidance and no mention of the sibling bill/rate tools (tw_electricity, jp_electricity, kr_electricity) to route between them.

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