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

Annotations already declare readOnlyHint=true, destructiveHint=false, and openWorldHint=false, so the safety profile is covered. The description adds useful context beyond annotations: no auth/account access, the 0–100 percentage domain, that volumes share the selected unit, and that source ethanol contents are measured rather than assumed.

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?

Front-loads the purpose, then adds shared constraints, then the mode-to-parameter mapping. Every sentence carries information and none is redundant with structured fields.

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 no explanation, and annotations cover the safety profile. The description fills the key gap (conditional mode parameters), though it leaves the distinct roles of highFuelEthanol versus pumpGasEthanol to be inferred.

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 78%, so baseline would be 3, but the description adds genuinely new meaning by specifying conditional per-mode requirements (e.g., fresh needs finalVolume; existing needs finalVolume/currentVolume/currentEthanol; correction needs tankCapacity/currentVolume/currentEthanol; ratio needs no volumes). The schema only marks five flat required params and does not encode these mode dependencies.

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 (Calculates) and resource (ethanol blend) and enumerates the four distinct modes (fresh, existing, correction, ratio), which differentiates it from sibling calculators like calculate_race_fuel_and_weight. An agent can identify exactly what the tool produces without opening the schema.

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?

Provides clear mode-selection guidance by mapping each mode to its required inputs, and notes it runs without authentication or account data. It does not name sibling tools or state when a different calculator should be used instead, so it stops short of full alternative routing.

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