Index constituents

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

Annotations already declare read-only, idempotent, open-world, non-destructive behavior, so the safety profile is covered. The description adds genuine behavioral context beyond that: the dual-mode semantics, the sort ordering driven by `sortBy`, and the data limitation that Thndr provides no index weights. It does not cover pagination/limit behavior or how an unrecognized index is handled.

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 the scope constraint and then the two modes, with dense field enumerations rather than prose. Every sentence carries information; the only mild drag is the parenthetical index list, which is useful but long.

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 correctly compensates by enumerating the fields returned in each mode (level/change%/member count vs sector/last/change/value/volume/market cap). It also flags the 'Egypt only' limitation. It omits return pagination and the interaction between `limit`/`sortBy`/`order` defaults beyond what the schema states.

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 60%, so the description must carry some weight — and it does: it explains the semantics of `index` (mode switch, with the EGX70→EGX70-EWI alias) and that results are sorted by `sortBy`. `limit`, `order`, and `market` details are left largely to the schema, which is acceptable at this coverage level.

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 (index constituents) and precisely defines two distinct behaviors keyed on whether `index` is supplied, including the returned fields for each mode. It also scopes the tool geographically ('Egypt only') and names concrete indices (EGX30, EGX70 EWI, Shariah), making it easy to separate from siblings like get_markets or search_instruments.

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 tells the agent how to trigger each mode: omit `index` to list indices, supply `index` to get member instruments. It adds the caveat that index weights are unavailable so the agent doesn't promise them. It stops short of naming an alternative tool for the related task (e.g. get_markets for broad market data).

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