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

Annotations only cover safety (readOnly/openWorld), and the description adds substantive behavior beyond them: the trade-date roll rule, determinism ('no AI'), the x402 payment model at $0.001 USDC per call on Base, and a 5-calls-per-day free quota per client. Pricing and rate-limit disclosure is exactly the extra context annotations cannot carry.

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, front-loaded with the core computation before defaults, roll behavior, and pricing. No filler, though the billing/quota sentence is somewhat commercial noise relative to the agent's selection decision.

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 deterministic date-arithmetic tool with no output schema, the description covers defaults, calendar semantics, roll behavior, and cost. It omits the return shape (a date string) and the legal values for the calendar identifier, but those are minor for a three-parameter read-only tool.

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% (t, calendars, trade_date all documented with examples and ranges), so the schema already carries the parameter burden. The description adds semantic meaning for t=1 (US equities since 28 May 2024) and the default calendar pair, but that largely restates schema content, matching the baseline 3.

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: computes a settlement date T+N from a trade date on a joint calendar, and names the roll-forward convention. However it never explicitly distinguishes itself from the close sibling add_business_days, which on a single calendar would do almost the same arithmetic, so the agent must infer the difference from the calendar/lag framing.

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?

Gives useful context for using the defaults ('t=1 (US equities since 28 May 2024)', default XNYS,FED) and describes the roll-to-next-business-day precondition. It does not say when to prefer this over add_business_days/is_business_day, nor name any exclusion, so usage is implied rather than prescribed.

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