Market clock

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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is fully covered structurally. The description adds that the answer is live status with UTC timestamps, but says nothing about caching/refresh semantics, holiday handling, or whether the next open/close accounts for early closes — modest added value over the annotations.

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 clause with the core answer front-loaded ('Whether the US equity market is open now') followed by the supporting detail. No filler or restated name/title content.

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 must hint at the return values, and it does: open/closed status plus next open and close in UTC. It omits timestamp format and timezone-edge handling, which is a minor gap for such a small, no-input 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?

The tool takes zero parameters, so the baseline is 4; there are no parameter semantics the description could or should document.

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 subject (US equity market open status) and the returned values (next open and close, UTC) in one sentence, which an agent can grasp immediately. It does not name or distinguish itself from the closest sibling, reference_calendar, leaving the split to inference.

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 explicit when-to-use or when-not-to-use guidance, and no mention of the alternative reference_calendar for schedule-style questions. For a zero-argument status tool the intended usage is strongly implied, but the description never states the condition that selects it over calendar lookups.

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