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

Annotations declare readOnly, idempotent, non-destructive, closed-world, so safety is covered. The description adds valuable behavioral context beyond that: 'yearly cost when the issuer publishes it' signals nullable data, the exchange-suffix convention for non-US tickers, and the not-found fallback to search_symbols. It does not mention rate limits or caching, but the additions go 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?

Front-loads what the tool returns, then usage routing, then the ticker format and fallback. Dense but every clause carries information. Slightly heavy for a one-parameter tool, but no wasted sentences.

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?

For a read-only single-ticker info tool with an output schema already covering return values, the description supplies the remaining context an agent needs: field scope, sibling disambiguation, ticker format, and failure recovery. Nothing material 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 single param is fully described in-schema, so baseline is 3. The description adds real value by explaining the exchange-suffix format with concrete examples (VWCE.DE, IWDA.AS) and by prescribing search_symbols as the recovery path for invalid tickers.

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: returns detailed reference data for a single fund or share. Lists the concrete fields returned (name, type, exchange, cost, return, volatility, worst fall, holdings, sectors), which distinguishes it from siblings like last_price (price only) and look_through (portfolio-level ownership).

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?

Explicitly says 'Use it before deciding whether a ticker belongs in a measurement,' then names two alternatives with when to prefer each: last_price for today's price only, look_through for whole-portfolio ownership. Also routes to search_symbols when a ticker is not found.

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