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

Annotations declare readOnlyHint and idempotentHint. The description adds behavioral details beyond annotations: it discloses that weekends and holidays are skipped, and it returns next open and close times. No contradictions.

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?

The description is two sentences with no fluff. The first sentence front-loads the core purpose and return format; the second sentence clarifies parameter semantics. Every sentence adds value.

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?

Despite no output schema, the description fully explains the return object structure. Parameter documentation is complete (exchange flexibility, at default and example). The context of 'fastest answer' and holiday handling covers all agent needs.

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%. The description adds significant meaning: exchange accepts names or IDs (case-insensitive), at parameter has a default and example usage ('will the NYSE be open at 3pm ET on Monday?'), which helps the agent use parameters correctly.

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 clearly states the tool checks if a stock exchange is open at a given time, specifies the return object (open, status, next open, close if open), and differentiates from siblings by positioning it as the fastest answer.

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?

The description provides clear context: it answers 'is <exchange> open?' quickly, and explains the optional 'at' parameter for specific moments. However, it does not explicitly state when not to use this tool versus alternatives like get_exchange_status or time_until_next_open.

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