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

Annotations already declare readOnly/idempotent/non-destructive/open-world, so the bar is lower, yet the description adds real operational context: walk-in policy, the post-authorization email workflow, and the datum that pageUrl is only populated for sites in the 48 tracked metros. That coverage caveat is exactly the kind of behavior an agent must know before promising a link.

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 front-loaded sentences that each contribute: what is found, how walk-ins/requisitions work, and the pageUrl caveat plus usage instruction. Slightly dense in the final sentence but no filler.

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 values need no prose, and the description still covers the one conditionally-present field (pageUrl, only in tracked metros) that an agent could otherwise misuse. For a 4-param read tool with full annotations, nothing material is missing.

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%, covering lab, zip, limit and radiusMiles with defaults and snapping behavior, so the schema carries the parameter burden. The description adds no syntax or format nuance beyond a mention of the ZIP, so baseline 3 applies.

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?

Specific verb 'find' plus a concrete resource ('Quest Diagnostics, Labcorp and BioReference patient service centers') scoped to a US ZIP, and it enumerates the returned fields (address, distance, phone, hours). No sibling tool covers this domain, so the agent can route here unambiguously.

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?

Gives situational context ('walk-ins are accepted at most sites', requisition arrives by email after physician authorization) and an explicit instruction for the pageUrl field: 'cite it when giving a location'. It does not name when-not-to-use or point at an alternative tool, so it stops short of a 5.

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