ETFs with price vs NAV

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

Annotations already declare read-only, idempotent, non-destructive, open-world behavior, so safety is covered. The description adds genuinely non-obvious behavior: the two sources return different column sets, Agah lacks several fund families, and all monetary values are in Rial. It stops short of describing what source='all' returns structurally (merged list vs. two blocks) or pagination semantics.

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 core purpose, then examples, then source payloads, then next-step routing — a logical funnel. The dense comma-separated field lists are justified given there is no output schema, though they read more like a spec dump than prose.

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 carries the return-shape burden and does so by enumerating columns per source and stating the currency. Remaining gaps are the combined behavior of source='all' and whether limit truncates across sources — minor but relevant for a dual-source listing 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 coverage is 100% and the schema already explains sort enums, source counts, and type families in detail. The description's only real parameter-level addition is the Rial currency unit; the per-source row lists describe return values rather than parameter meaning, so baseline 3 applies.

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 ("List exchange-traded funds") plus the distinctive fields it returns (price, NAV, gap/bubble, traded value, returns). The per-source row breakdown and the closing routing line separate it from br_screener, br_fund and br_stock without requiring the agent to open any schema.

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?

Gives concrete task examples ("cheapest gold ETF", "fixed-income ETF with the lowest bubble") and explicit alternatives with the condition that selects them: br_stock/br_fund for a single fund, br_screener for arbitrary column filtering. The agent can route correctly from this text alone.

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