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

Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), and the description adds genuinely new behavioral facts: accent-insensitive matching, the rule that every word of 3+ letters must appear, and active registrations being ranked before deregistered ones. Those details change how an agent forms a query and interprets result order.

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?

Purpose and scope come first, then matching behavior, then ordering, then the optional geographic filter — a sensible front-loaded order with no filler sentences. The ubigeo clause is the longest but carries its examples efficiently.

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?

An output schema exists, so return values need no explication, yet the description still summarizes them ('RUC, name, status and address so you can pick the right one'). Combined with the entity-type restriction, ranking order, and matching rules, an agent has everything needed to call this correctly on the first try.

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 adds matching semantics the schema does not state (accent-insensitivity and the all-words-must-match rule for 'name'). The ubigeo prefix explanation largely duplicates the schema's own 2/4/6-digit documentation, so it is an addition of marginal value rather than a full level-up.

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 ('Search SUNAT's published taxpayer register by company name') and immediately delimits scope: legal entities only (RUC prefix 20 plus government offices), natural persons never returned. That boundary is exactly what distinguishes it from a generic entity/registry lookup among the siblings.

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?

Gives clear context for when this applies (querying by company name, contrast with number-based lookup implied by the pe_ruc sibling) and an explicit exclusion: natural persons are excluded entirely. It stops short of naming an alternative tool for natural-person or RUC-number queries, so routing to a sibling still requires inference.

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