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

Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the bar is lower. The description nonetheless adds genuine behavioral context: the overlap is computed from full issuer holdings files matched on ISIN, which tells the agent the numbers are point-in-time holdings-based rather than price-based, and that tickers must be resolvable by ISIN.

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, front-loaded with the definition of the headline metric and its formula in parentheses, then data provenance, then example queries as a routing cue. No filler and nothing repeated from the title or 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?

With an output schema present the description needn't enumerate return fields, and it instead defines the metric precisely enough to interpret those fields. The only shortfall is that it doesn't distinguish this from the closest sibling tools (compare, etf_holdings), a minor gap for a simple 3-parameter analytical tool.

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 100%, with each of fund_a, fund_b, and limit documented including format and bounds, so the baseline is 3. The description only lightly reinforces parameters via "the largest shared holdings" (implying limit shapes that list) without adding format or edge-case guidance beyond the schema.

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?

Names a specific resource (two ETFs) and defines the exact computation: overlap by weight as the sum of the smaller weight over commonly held companies, plus shared count, per-fund shared share, and largest shared holdings. An agent can distinguish this from compare or etf_holdings purely from this text.

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?

Ends with quoted example intents ("VOO vs QQQ overlap", "is IVV the same as VOO") that imply when to reach for it, and the ISIN-matched full issuer file note hints at data fidelity. But it never states when NOT to use it or names the sibling (compare, etf_holdings) that handles adjacent questions, so routing is left to inference.

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