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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the bar is lower — yet the description still adds real behavior: only COMPLETED periods count and the in-progress week/month is excluded, computed from official NSE closing levels, and sorting is best-to-worst cumulative. It does not mention pagination, caching or rate limits, keeping it short of 5.

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 core action, output format, universe and usage triggers in a logical order — good structure. The long inline enumeration of sectoral indices (IT, Bank, Auto, Pharma, FMCG...) consumes tokens without changing agent behavior and could be trimmed, making it slightly verbose rather than wasteful.

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 carries the return-value burden, specifying per-period % plus cumulative % and the sort direction. Combined with the completed-period exclusion rule and catalog scope, an agent has everything needed to call this correctly; the absence of an output schema is fully compensated.

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 description coverage is 100%, so the baseline is 3; every parameter (limit, order, periods, category, granularity, index_names) is already documented in the schema, including the 'sectoral for sector rankings' guidance. The description adds only marginal param context (cumulative sorting, ~140-index catalog coverage) and no syntax or edge-case detail beyond the schema.

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 — 'Rank NSE indices by RETURN over recent completed weeks or months, using official NSE index closing levels' — and defines the output shape (per-period % plus cumulative %, sorted best-to-worst). An agent can distinguish this from get_index_history or get_market_pulse purely from the description.

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 enumerates triggering phrasings ('rank sectoral indices by 3-week return', 'which sector performed best last month', 'top gaining sectors') and adds a negative rule: do NOT compute a sector return from its constituents, which is only an approximation. This is a textbook when/when-not statement.

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