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

While the annotations cover safety (readOnlyHint: true), the description adds crucial behavioral context by specifying that the data is the 'full reported holdings' as of the 'fund's own as of date,' providing temporal context and granularity.

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 highly efficient. Both sentences contain dense, non-redundant information, front-loading the core purpose and the critical sibling differentiation.

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?

Given the complexity of financial holdings (ETFs, cash, futures, specific set of assets), the description is entirely comprehensive, covering scope, data freshness, granularity, and exclusion criteria.

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?

Though the schema is 100% covered, the description adds significant semantic value by specifying the types of positions returned (cash, collateral, futures) and explaining the purpose of the asset_class field (to prevent silent mixing).

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 defines the tool's scope to six specific iShares ETFs and distinguishes its function—providing full holdings—from the sibling tool 'index_constituents' by explicitly stating the purpose of each.

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 provides a crystal clear 'when to use' guideline: 'For just the equity index membership, use index_constituents instead,' which effectively routes the agent away from this tool when appropriate.

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