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

Adds genuinely useful behavior beyond the annotations: the credit model ('charges 1 credit only when the person is found with an email or phone') and the side effect that saveToContacts persists the person to contacts, which explains why readOnlyHint is false despite the read-like name. It stays silent on rate limits and result freshness, so not a 5.

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?

Four tight sentences with the purpose front-loaded, followed by return contents, scope constraint, and billing behavior. No sentence is redundant with the name/title and nothing is padded.

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 an output schema present, the brief return summary is sufficient, and the billing plus scope caveats cover the main decision-relevant facts. It could still specify which standalone identifiers (email alone, LinkedIn alone) are valid without a domain, but the core is complete.

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 100%, so the schema already documents all five parameters including the 'needs domain' constraint on name. The description only echoes the identifier list and adds a note on saveToContacts, so baseline 3 is appropriate.

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 (look up), cardinality (one person), and the exact identifiers accepted (LinkedIn URL, email, name + company domain). This distinguishes it from plural siblings like persons_search and the narrower persons_find_email/persons_find_phone without the agent needing to open any 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?

Provides a clear scope boundary — 'professional contacts only: people in their role at a company, not private individuals' — which tells the agent when this tool will fail. It does not, however, route the agent among alternatives such as persons_search for broader matching, leaving sibling selection to inference.

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