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

Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint, so safety is covered. With no output schema present, the description steps in and specifies what the response contains (average returns, sector breakdown, top/bottom performers), which is real added value beyond the structured fields; it still omits the time window and any response-sizing caveats.

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?

One front-loaded sentence naming the resource and its return contents, followed by a compact Args block for the single parameter. No filler, though the Args block is slightly redundant with the parameter name already exposed in the schema.

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 single-parameter, no-output-schema read tool this covers the essentials: what is returned and what values the parameter accepts. The notable gap is the performance horizon (daily, YTD, trailing?) – critical for interpreting 'average returns' – plus no positioning against get_market_movers/get_sector_analysis.

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 0% – the property is just a bare string with default 'us' – so the description has to carry the load, and it does by enumerating valid market codes ('us', 'ca', 'uk', 'de', 'il', 'au', 'hk', 'sg', etc.). The open-ended 'etc.' and lack of a canonical full list keep it short of a 5.

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 verb and resource ('Returns market-wide performance for a specific country') and enumerates the payload ('average returns, sector breakdown, top/bottom performers'). It does not explicitly distinguish itself from near-neighbours like get_market_movers, get_sector_analysis, or get_market_commentary, so the agent must infer the boundary.

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 phrase 'market-wide' and 'for a specific country' – the agent can guess this is the country-level aggregate rather than a single-ticker or sector call. There is no explicit when-to-use, when-not-to-use, or named alternative among the many market/sector siblings.

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