Find eToro instruments

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

Annotations already establish readOnly/idempotent/openWorld/non-destructive, so the safety profile is covered. The description adds genuinely useful behavior beyond that: the lack of free-text search, the exchange-suffix convention for ETFs with a concrete example (CSPX.L), and the return field list (no output schema exists, so this is the only source).

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?

Three dense sentences with no filler, front-loaded with the core action before the constraints. The return-field list and the 'not both' rule each carry weight, though the sentences are packed tightly enough that a little breathing room would help readability.

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 supplies the return shape itself, and it covers the input modes and mutual-exclusion rule. Remaining gaps are minor: it never says what happens when no parameters are supplied (full listing?) or how pageSize pagination behaves.

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 only 25% (just 'symbols'), so the description does meaningful compensation: it clarifies symbols are exact tickers, contrasts symbols vs instrumentIds, explains the ETF suffix format, and notes only one of the two should be supplied. pageSize and the type enum values are left to the schema, which documents them adequately.

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 ('look up instruments') and enumerates the three lookup modes (exact symbols, instrument ids, or by type). Also names the returned fields (instrumentId, symbol, displayName, type, exchangeId), so an agent knows exactly what it gets. Clearly distinct from the sibling portfolio/order/rate tools.

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 operating constraints: free-text name search is not supported, and symbols/instrumentIds should not be combined. These are real usage rules that steer the caller. It does not name an alternative tool, but none of the siblings overlaps this lookup function, so the guidance is effectively complete.

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