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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so safety is covered. The description adds genuinely non-structured context: it is a typical-usage estimate rather than a measurement, it works for any oil tank, and it needs no location — which prevents an agent from hunting for a location parameter.

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 tight sentences ordered as trigger, inputs/outputs, then caveat — the most decision-relevant information (when to call) is front-loaded. No filler, and the return payload is itemised in a single clause.

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 simple, read-only, three-parameter calculation with no output schema, the description covers everything needed: when to call it, what it consumes, what it returns (litres, cautious days remaining, suggested top-up, urgency), and the accuracy caveat. Nothing an agent needs before calling is missing.

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 all three parameters are already documented with ranges, defaults and enum meanings. The description's 'tank size, how full it is and rough daily use' merely paraphrases those fields and adds no format or unit detail beyond the schema, so the 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?

The description opens with a specific verb+resource pairing — estimating how long the oil in a tank will last — and frames it as a planning/ordering forecast. That is clearly distinguishable from the sibling price-lookup tools and from tankful_delivery_request_draft, so an agent can route 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?

Trigger conditions are stated explicitly: 'when someone asks how long the oil in their tank will last, when they need to order, or how much to order.' This is clear positive guidance, but it never names a sibling or states when not to use it — e.g. that actual ordering belongs to tankful_delivery_request_draft.

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