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 mechanism (x402 on Base, $0.001 USDC per call), the rate limit (first 5 calls/day/client free), determinism ('no AI'), and that skipped holidays are returned. For an agent that must decide whether a paid call is warranted, this is exactly the extra behavioral context needed.

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 sentences, no filler. Core semantics lead, the pricing/rate-limit facts follow, and every clause (negatives, calendars, skipped holidays, cost) carries information an agent needs before invoking.

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 3-param stateless computation with no output schema, the description covers purpose, calendar semantics, return content, determinism, and cost, which is close to sufficient. It omits error/boundary behavior (e.g., what happens with an invalid calendar alias), leaving only minor gaps.

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 genuinely adds meaning the schema does not: it makes explicit that negative 'days' values subtract rather than error, and frames the calendars argument as a joint-calendar AND semantics. It does not add format/alias detail beyond what the schema already documents.

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 (add/subtract N business days to a date), clarifies that negative days subtract, and names the joint-calendar scope (NYSE, Fedwire/FedACH, TARGET2, UK). It lets an agent distinguish this from business_days_between and settlement_date, but it never names a sibling directly, so it falls short of the 5 bar.

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?

No when-to-use or when-not guidance and no routing to siblings such as adjust_date or settlement_date, which are the closest alternatives. The pricing/free-tier sentence tells the agent the cost of calling, not when to choose this tool over another.

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