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

Annotations already declare readOnly, idempotent, openWorld, and non-destructive, so safety is covered. The description adds the useful constraint that at least one identifier is required (the schema marks none as required), but says nothing about lookup success/failure behavior or rate limits.

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, front-loaded sentences with zero waste: purpose, inputs, and the constraint in that order. Every sentence earns its place.

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 simple two-parameter lookup with no output schema and full annotation coverage, the description is largely complete. It would be stronger if it hinted at what a result looks like (found vs not found) or referenced the related find_email tool.

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 schema already documents both parameters with examples. The description adds a small amount by clarifying the 'and/or' combination relationship and the minimum-identifier requirement, but provides no format details beyond what the schema gives.

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 (Find) and resource (mobile phone number), which clearly distinguishes it from sibling find_email. However, it does not explicitly name or contrast against that sibling, leaving the differentiation to inference.

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 usage by listing accepted identifiers and the 'at least one required' constraint, giving a usable sense of when it applies. But it offers no explicit when-to-use vs alternatives guidance and does not mention find_email or validate_email as related tools.

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