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

Annotations already declare readOnly, idempotent, non-destructive, open-world behavior, so the safety profile is covered. The description adds genuinely useful context beyond that: it is free with no API key required, and it wraps entity_lookup with a preview mask, telling the agent results are a restricted subset rather than the full record. It does not explain how the preview differs in scope (which fields are masked), leaving a small gap.

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 high-value fact (FREE, no API key) is front-loaded and the description is short. However, sentence two largely repeats sentence one's purpose statement ('read one company's free registry preview by its id' vs 'Fetch one company's free registry preview by the id returned by search'), so it is not entirely waste-free.

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 single-parameter, read-only lookup there is little missing: an output schema exists so return values need not be spelled out, and annotations carry the safety profile. The only substantive omission is what the 'free preview mask' actually withholds compared with entity_lookup or get_full_dossier, which would help an agent decide whether to escalate.

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?

The schema already documents the single id parameter at 100% coverage, including the same 'CIF/NIF, EU VAT or LEI' guidance. The description restates that rather than adding format details, so the schema is doing the work and this sits at the baseline.

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?

Names a specific verb and resource ('read one company's free registry preview by its id') and distinguishes itself from siblings: it is used after search, accepts search ids or CIF/NIF/EU VAT/LEI, and is explicitly framed as entity_lookup with the free preview mask. An agent can select it without opening the schema.

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 a clear usage chain ('Use after search to read one company's...') and lists acceptable id types, which is effective context. It stops short of explicitly saying when not to use it — e.g., when the paid full record from entity_lookup or get_full_dossier is warranted — so the alternative routing is only implied.

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