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

Annotations already establish read-only, idempotent, non-destructive, closed-world behavior, so the description only needs to add context — and it does: cached data refreshed every 12 hours (implying possible staleness) and zero cost. It does not discuss any rate limits or failure modes, but for a free read-only snapshot those gaps are minor.

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 what it returns, then routing, then cost. Slightly dense but every clause carries information; 'free and carries no charge' is mildly redundant with 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?

With no output schema, the description compensates by naming the exact return fields (national median/p10/p90, per-state percentiles, savings context), the caching cadence, and sibling alternatives. An agent has everything needed to call it and interpret results.

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 100% and the schema already documents both optional params as state-selection hints. The description restates that origin/destination only drive which per-state percentiles are returned, which reinforces but does not materially extend the schema. Baseline 3 is appropriate.

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 and resource (cached US diesel market snapshot) plus the data source and refresh cadence, and enumerates the returned aggregates (national median/p10/p90, per-state percentiles). It is immediately distinguishable from optimize_fuel_plan and the Diesel Prices tools.

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?

Explicitly says when to use it (market questions or cost estimates) and names two alternatives with the conditions that select them: optimize_fuel_plan for stop-by-stop plans and Flow Diesel Prices for posted truck-stop prices. Nothing is left to inference.

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