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

Annotations already mark it read-only and non-destructive, but the description goes beyond them by disclosing critical behavior: first/last points are always kept, the series is evenly downsampled and never a tail slice, points[0].v matches get_fund's inception index price, and no auth is required. This is useful context well beyond annotations with no contradiction.

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?

The description is concise for the amount of nuance it conveys and front-loads the core purpose, then adds essential behavioral caveats and the key sibling distinction. Every sentence contributes useful selection information and there is no redundant or filler content.

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 present, the description explains the return shape as '[{t, v}] points' plus exception cases and per-fund nuances. Auth requirements are explicitly stated as none, and the key limitation (no history for FTA-STOCKS/EVENT-CARD) is covered, so the agent has enough context to invoke and interpret the tool correctly.

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%, so both parameters are already documented with clear descriptions. The description adds interpretive context around returned data rather than the parameters themselves. It reinforces the meaning of what a requested point count yields but does not significantly expand parameter semantics beyond the schema, so baseline 3 is appropriate.

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?

The description states a specific verb and resource: 'Index history for one fund as [{t, v}] points.' It also clarifies exactly what kind of history is returned and distinguishes it from the sibling get_fund tool for current numbers. The tool's role is immediately distinct from other history/fund 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?

The description explicitly tells the agent when to use an alternative instead: 'FTA-STOCKS and EVENT-CARD have no history series — use get_fund for their current numbers.' It also explains context such as downsampling and which funds have which data characteristics, leaving little ambiguity about selection.

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