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

Annotations already declare readOnly/idempotent/non-destructive, so the safety burden is lifted, and the description adds real behavioral context beyond them: the default index, the weekly sampling frequency (not present in the schema), and the default 5-year window. It stops short of covering data freshness, rate limits, or return shape.

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-loaded with what the tool returns and its defaults before the input-format detail. The enumerated slug/code list is verbose but earns its place by disambiguating a string-or-number parameter; 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?

With only two optional parameters, no output schema, and no nesting, the definition covers enough: what metrics come back, the default scope, and how to address indexes. It could be more complete by noting the return granularity or how the time series is shaped, but that gap is minor for a read-only metrics endpoint.

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 the baseline is 3, but the description genuinely adds meaning by mapping slugs to numeric codes (nifty-50 → 13, nifty-bank → 25, etc.) that the schema only refers to abstractly. The 'years' max-20 constraint is left to the schema, so it is not fully additive.

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 ('Get index valuation metrics (PE, PB, Dividend Yield) over time') with concrete defaults, so the agent knows exactly what it returns. It does not, however, distinguish itself from adjacent siblings like get_index_performance or get_index_history, which an agent could plausibly confuse it with.

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 gives an implied use case ('assessing whether the market is overvalued or undervalued relative to historical averages'), which is genuine context, but it never states when to prefer this over get_index_performance, get_index_history, or get_market_pulse, nor any exclusions. Usage is inferable but not directed.

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