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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so the safety profile is covered. The description adds genuinely useful context beyond them: the estimate is free, it uses account pricing, and it deduplicates valid numbers rather than performing lookups.

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 dense sentence with the most decision-relevant fact ('Free') front-loaded and no filler. It is terse to the point of being elliptical, but nothing 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?

An output schema exists, so return-value explanation is unnecessary, and the description covers cost and non-lookup behavior. However, with 0% schema description coverage it leaves the products enum and include_sms_assessment undocumented and gives no guidance on when a quote should precede a real lookup.

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 0% across 3 parameters. The description implies phone_numbers are validated and deduplicated, which adds some meaning, but products and include_sms_assessment receive no explanation anywhere, leaving the agent guessing about the enum options and the SMS assessment flag.

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 states a specific action (free estimate of lookup cost) and a key constraint (no lookup is performed), which cleanly separates it from the lookup siblings like vri_bulk_lookup and vri_number_lookup. It is clear but leans on the title 'Estimate lookup cost' to fully name the resource.

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 'free' and 'no lookup' phrasing suggests calling this before committing to a paid lookup or submit_job, but there is no explicit when-to-use or when-not-to-use statement and no sibling is named as an alternative.

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