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

Annotations only declare readOnlyHint and openWorldHint; the description goes well beyond them by disclosing the payment model ($0.002 USDC per successful call via x402 on Base/Solana/Arc), that failed calls are free, that tariffs are not fetched, and the day-counting convention (calendar days, start day included unless countStartDay is set). Those are exactly the traits an agent needs before invoking a paid tool.

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?

Purpose is front-loaded in the opening clause, followed by inputs, outputs, caveats and pricing in a tight single paragraph with no filler. The one long sentence is dense but every clause carries information; slight readability cost keeps it from a 5.

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?

Output schema exists, so return values need no explanation, yet the description still summarizes them; combined with the counting rule, the tariff-not-looked-up caveat and the x402 payment terms, an agent has everything needed to call this correctly and predict the cost.

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% so the baseline is 3, but the description adds genuine meaning: it maps start/end onto the demurrage vs detention lifecycle and shows the rate tier string syntax ('1-4:75,5-8:150,9+:250') with an open-ended final tier. Only the currency and containers parameters get no extra narrative.

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+resource (container demurrage/detention calculator) and enumerates both the inputs it consumes and the outputs it produces (chargeable days, tier split, totals per container and aggregate). No sibling tool covers demurrage/detention, so it is unambiguously distinguishable from the rest of the logistics/energy set.

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?

Explains the mode-dependent semantics of the dates (discharge or gate-out for demurrage vs gate-out or empty return for detention) and explicitly warns 'Carrier tariffs are not looked up', telling the agent it must supply rates itself. It does not name an alternative tool to use for tariff lookups, so it stops short of full when-not guidance.

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