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

Goes well past the readOnlyHint/openWorldHint annotations: states that values are indicative public assessments rather than firm offers, that ex-wharf prices exclude freight and taxes, that only VLSFO is covered, and that billing is $0.002 USDC per successful x402 call with failed calls uncharged. This is exactly the kind of context an agent cannot infer from structured fields.

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?

Two dense sentences that front-load the data scope before the caveats and billing note. No wasted clauses, though the payment/pricing sentence is standard boilerplate that could be trimmed for a high-frequency caller.

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?

Covers scope, data provenance, limitations, and cost, and an output schema exists so return shape needn't be described. Missing only operational detail such as update cadence or data staleness, which matters for a daily-published price page.

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 single optional 'port' parameter is already documented, including the empty-returns-all behavior and the region example. The description's phrase 'by port and regional average' reinforces that partial region matching is supported but adds little the schema lacks.

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?

Names a specific resource (VLSFO bunker fuel prices in USD per metric ton), the source (Ship & Bunker public prices page), and the exact fields returned (price, change, daily high, low, spread). Clearly separable from siblings like energy_crude_oil_brent_wti or logistics_jet_a1_fuel_index.

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 implied by the scope statement ('Only the VLSFO grade is extracted') and the marine-fuel domain, but there is no explicit when-to-use / when-not-to-use guidance or pointer to an alternative tool for other grades or spot marine fuel.

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