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

Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so the safety profile is covered. The description adds genuinely useful behavior — the default window, the adjustable range, and the roughly 10-year depth limit for domestic main share classes — but says nothing about return ordering, currency, or dividend adjustment.

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?

A single compact line that front-loads the scope and parenthesizes the parameter constraints. The bilingual tail is mild redundancy but aids cross-language disambiguation; nothing else is wasted.

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 two-parameter lookup with no output schema, the key gaps are the meaning/format of code and what the returned series looks like (fields, granularity, currency). The description covers the temporal window well but leaves the required parameter half-specified.

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 0%, so the description must compensate. It does well for months (default 12, allowed 1-120), but code is left completely unexplained — no format, no example, no indication of what identifier is expected.

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 pairs a specific verb with a specific resource — a daily NAV time series for a fund — which is distinguishable from siblings such as etf_price_history or fund_lookup. It does not explicitly name those siblings, but the resource is unambiguous.

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?

Usage is only implied: the mention of a default 12-month window and a 1-120 range hints that this is for historical series retrieval, but it never says when to choose this tool over fund_lookup or etf_price_history, nor any prerequisites.

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