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

Annotations cover the safety profile (destructiveHint=false, idempotentHint=true, openWorldHint=true), so the bar is lower. The description adds genuinely useful behaviour beyond them: the data source (domain registration records) and a concrete cost model ('10 credits if found, free otherwise') that an agent needs for budget-aware decisions. It does not explain the surprising readOnlyHint=false, but that gap is minor.

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?

Two tight sentences, front-loaded with the identity of the resource and followed by the cost consequence. No filler, nothing redundant.

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 two-parameter lookup with annotations covering safety, the description gives the return content (names, phone numbers) and the billing model, which is much of what matters. However, with 0% schema coverage it leaves bypass_cache unexplained and says nothing about result shape or miss behaviour beyond the free/charged distinction.

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% for two parameters. The description implies the 'email' input but adds no format expectations, and 'bypass_cache' is completely undocumented in both the schema and the description, leaving an agent unable to judge when to force a fresh lookup.

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: reverse-look up an email address to find the person behind it, returning names and phone numbers from domain registration records. That is clear and distinguishable from verify_email, but the description never explicitly names verify_email or reverse_phone as the near neighbours an agent might 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?

There is no when-to-use or when-not-to-use guidance. An agent has to infer from the phrase 'who is behind an email address' that this is an identity/attribution lookup rather than a deliverability check, and nothing tells it when to prefer verify_email or reverse_phone instead.

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