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

Annotations already declare readOnlyHint and openWorldHint, but the description adds genuinely non-structured context: pricing ($0.002 USDC per successful call, paid via x402 on Base/Solana/Arc) and that failed calls are not charged. That billing model is exactly the kind of behavioral trait annotations cannot convey. It stops short of describing response shape or coverage/rate limits, hence not a 5.

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 and data source are front-loaded in the first clause, followed by scope limits and cost. Dense and largely waste-free, though the payment details are packed into one long semicolon-heavy sentence that could be split for faster scanning.

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 read tool with an output schema, the description covers source, aggregation semantics, scope exclusions, and cost. The only meaningful omission is guidance on obtaining a facility id when the caller doesn't have one, which matters because facility search is explicitly out of scope.

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?

Only one parameter, fully described in the schema ('GHGRP facility id, digits only, e.g. 1000001'). The description restates the id and example but adds no new constraint beyond the schema, so baseline 3 applies.

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+scope: EPA GHGRP reported emissions for one facility by year, sourced from EPA Envirofacts. The aggregation basis (CO2e summed across gases per year, as published) is stated, which distinguishes it from sector-level or registry-wide siblings like energy_epa_echo_enforcement.

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?

The description gives scope exclusions ('Facility search and sector breakdowns are not included') and the required id form (GHGRP facility id, e.g. 1000001), which implies when it applies. But it never names what to use for facility lookup or sector breakdowns, so the agent must infer alternatives from the sibling list.

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