get_market_status

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

Annotations already declare readOnlyHint, idempotentHint, non-destructive and openWorld, so the safety profile is covered. The description's one real addition is the US-market scoping (it will not answer for international exchanges) plus a summary of returned fields. That is useful but thin; nothing is said about holiday handling or timezone of the reported time.

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?

Two sentences, purpose front-loaded, nothing wasted. The 'Returns:' block is mildly redundant since an output schema already exists, which keeps this just short of a 5.

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 zero-argument status check with a full output schema and annotations covering safety, the description supplies everything an agent needs to decide and invoke. Remaining details (timezone, holiday calendar) are minor and partly covered by the output schema.

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 there is nothing for the description to disambiguate. Baseline 4 applies; the description correctly does not invent parameter guidance that does not exist.

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 precise verb and resource: 'Check if US stock markets are currently open.' No sibling tool (e.g., get_api_status, get_market_summary, get_market_indices) covers open/closed market state, so the purpose is unambiguous without opening any schema.

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 only implied by the purpose itself — an agent infers it should call this when it needs to know whether US markets are trading. There is no explicit when-to-use statement, no prerequisites, and no reference to alternatives such as get_api_status for service health.

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