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

Beyond the readOnly/idempotent annotations it discloses the return shape (every pair ranked by weight overlap, shared share, common-company count, holdings date/source), the measurement method (shared holdings, not return correlation), and rich degradation behavior: uncovered tickers named and skipped, and a long list of non-comparable ETF categories each with a reason. This is substantive behavioral context annotations never convey.

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?

Front-loaded with the usage trigger and organized from purpose to output to edge cases to exclusions. Dense but nearly every sentence carries unique information; the long enumeration of non-comparable categories is verbose yet genuinely useful for interpreting partial results.

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 an output schema present the description need not detail return values, yet it still characterizes them, and it covers inputs, semantics, failure modes, and alternatives. Nothing an agent needs to select or invoke this tool correctly is missing.

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% and the schema already documents the 2-30 range and the 'two give one pair' behavior, so the description largely restates structured fields. It confirms the ticker semantics but adds no format or edge-case detail the schema lacks, making baseline 3 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?

States a specific verb+resource (produces an overlap matrix across 3-30 US ETFs) and the user intent it serves (duplicate detection, diversification check). It explicitly distinguishes itself from the two nearest siblings, get_etf_portfolio_lookthrough and get_etf_portfolio_risk, so an agent can route without opening schemas.

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?

Front-loads the trigger ('user lists three to thirty US ETFs... asks which duplicate each other'), covers the degenerate two-ticker case, and names explicit not-for alternatives with their own use cases. When-to-use, when-not, and alternatives are all present.

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