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

Annotations cover the safety profile (readOnlyHint=true), so the bar is lower, and the description adds real substance: it discloses that both GHG Protocol methods are computed, the factor sources (eGRID subregion, Green-e residual mix), and how renewable_kwh is treated as zero in the market-based result. It also states the return payload (kg CO2e per method with factors used), which matters since there is no output schema.

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?

Three sentences, front-loaded with the core action and inputs before method detail. Every clause carries information (methods, factor sources, REC/PPA treatment, return format) with no filler or restatement of the title.

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 read-only calculator with no output schema, the description adequately explains inputs, methodology, and the shape of the result. Gaps are minor: no mention of the year parameter's effect on market-based results, and no note on whether results are annualized or single-period, but the essential calling information is present.

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 description coverage is 100%, so the baseline is 3; the schema already documents kwh, zip pattern, year enum, and renewable_kwh. The description echoes the contractual-instrument semantics of renewable_kwh but adds no syntax or interaction detail beyond what the schema states, and never mentions the year parameter.

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 a specific verb (Calculate), a specific resource and scope (Scope 2 CO2e for a facility), and the exact inputs (ZIP, kWh) plus both accounting methods. It clearly distinguishes itself from the sibling calculate_fuel_emissions by being the electricity/Scope 2 tool.

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: the agent can infer this is the tool for electricity-based Scope 2, but nothing states when to pick it over calculate_fuel_emissions, compare_sites, or lookup_emission_factor. No exclusions or prerequisites (e.g., US-only ZIP, year constraint) are framed as usage guidance.

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