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

With no annotations, the description carries the behavioral burden and does well: it explains that status is evaluated against real trading hours and today's holidays in each exchange's timezone, lists the next_open_at/next_close_at fields, and notes the plan requirement. It omits rate-limit/error behavior and full response shape.

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?

Four sentences, front-loaded with the core purpose, then behavior, parameter usage, and prerequisite. No repetition or filler.

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 one-parameter status tool with no annotations or output schema, the description covers purpose, evaluation logic, key return timestamps, and access prerequisite. It could be slightly more complete about the full response shape, but it is sufficient to invoke correctly.

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 single schema parameter is undocumented in the schema, but the description fully supplies its meaning: a MIC code such as XNYS, optional, and omitting it returns all markets. That is exactly the missing semantic context.

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 first sentence names a specific resource (exchanges) and a specific status output (live open/half/closed), and situates it against real trading hours, holidays, and timezone. That is enough to separate it from sibling holiday/calendar tools such as trading_holidays or list_exchanges.

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?

It gives actionable scoping instructions—MIC for one market, omit for all—and states the plan prerequisite. It does not explicitly name when to prefer it over siblings or when not to use it, so it falls short of full routing guidance.

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