Market calendar

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

Annotations already declare readOnly, idempotent, non-destructive, openWorld, so the safety profile is covered. The description adds genuinely new behavioral context: times are converted from New York to UTC, early closes are included, and a settlement date is returned. That is meaningful disclosure beyond the structured fields, though pagination and response shape are unaddressed.

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?

A single dense sentence with the resource and range front-loaded before the output details. It is slightly overloaded with parenthetical asides, but every clause carries information and nothing is padded.

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?

With no output schema, the description usefully enumerates what comes back (core and extended session times, early closes, settlement date), which is what an agent needs to decide whether to call it. Only pagination/volume limits and timezone-format edge cases are left implicit for a two-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% and both parameters already document their defaults ('today, UTC' and 'start + 31 days'). The description's restatement of the default range mirrors the schema rather than adding syntax or format nuance, 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 states a specific resource (US equity trading days) and the concrete payload (core open/close and extended session times, settlement date), which is far more than a restatement of the name. It does not explicitly name or contrast with a sibling tool, but no sibling competes for the calendar concept, so differentiation is implicit.

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 reference_ prefix and the calendar framing, but the description never says when to reach for this versus reference_clock or the market data tools, nor does it state prerequisites. Adequate context, no explicit when/when-not guidance.

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