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

Annotations cover the safety profile (idempotent, non-destructive, open-world) but the description adds genuinely new operational facts: results are match levels only, underlying records are never returned, and each call costs 1 credit. The credit cost is the most valuable disclosure for an agent planning calls.

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?

Three short sentences, front-loaded with the core operation, then the return contract, then the cost. No filler or restatement of the tool name.

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 usefully defines the return shape (match / partial / no_match) and the credit cost, which is exactly what an agent needs here. The one gap is default_country, which neither the description nor the schema explains.

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 0%, so the description carries the full burden. It conveys that email identifies the records and name/phone are the compared fields, but default_country is never mentioned or explained, and no format hints (phone normalization, country codes) are given.

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 (check) plus the exact resource and comparison basis: name/phone against domain registration records that list the email. That scoping is distinctive enough to separate it from siblings like verify_email, reverse_email, and validate_phone.

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 implies the use case (contact verification) but never states when to choose this over verify_email, reverse_email, or validate_phone, nor any precondition or exclusion. The 'name and/or phone' phrasing hints at the inputs but not the routing decision.

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