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

Annotations already declare the tool read-only and non-destructive. The description adds meaningful behavioral context: output comes via ETF vehicles, EM is approximated from country funds, and the matrix mirrors a known website page. This gives an agent useful modeling limitations beyond 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?

The description is compact and front-loaded with the core output, followed by method, caveat, and update cadence. Each sentence contributes useful information, though the phrase 'The decomposition institutions see' is slightly stylistic rather than purely functional.

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 does a reasonably good job clarifying what will be returned: sector returns per region, plus leaders and laggards. It also notes the EM approximation and cadence. It could mention exact output formatting or whether all regions are returned by default, but the essentials are covered.

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?

Both parameters already have descriptions against schema enums, so schema coverage is 100%. The description restates the regions and windows but adds little semantic depth beyond what the schema provides. A baseline score of 3 is appropriate.

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 specific output: an 11 GICS sector × 4 region return matrix with leaders and laggards, which is concrete and distinguishable from generic market tools. It does not explicitly position itself against siblings such as compare_indices or get_index_snapshot, but the resource and scope are clear.

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 usage context: use it to see sector performance across US, Europe, Asia-Pacific DM, and EM over a selected window. It adds refresh timing ('Daily after each regional close') but does not explicitly discuss when not to use it or which sibling tool to choose instead.

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