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

Annotations already declare readOnly, idempotent, and non-destructive hints. The description adds valuable behavioral context: the data is cached and refreshed every 12 hours, it returns specific percentiles, and it selects states based on origin/destination. It also mentions 'typical optimized-savings context' as an extra output. No contradictions with annotations.

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 description is concise and front-loaded: the first sentence states what the tool is and its refresh cadence, the second describes output, the third gives usage guidance and alternative, and the fourth mentions cost. Each sentence earns its place with no fluff.

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 snapshot tool with two optional parameters and no output schema, the description is complete. It explains the returned data (national and per-state percentiles), how states are chosen, the caching behavior, and the no-charge aspect. An agent has enough to decide when to call and what to expect.

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?

The schema already provides 100% coverage of both parameters, describing them as optional place strings used to pick states. The description reinforces this ('for any states mentioned in origin/destination') but adds no new semantic information beyond the schema. Baseline 3 is appropriate since the schema does the heavy lifting.

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 clearly states the tool's function: a cached US diesel market snapshot providing national and per-state percentiles. It uses a specific verb ('returns') and resource, and distinguishes itself from the sibling optimize_fuel_plan by naming what it does not do (stop-by-stop planning). This leaves no ambiguity about the tool's purpose.

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 states when to use this tool ('market questions or cost estimates') and when to use the alternative ('optimize_fuel_plan when you need an actual stop-by-stop plan'). It also notes the tool carries no charge, which is relevant for cost-sensitive decisions. This is clear routing guidance.

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