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

Annotations already declare readOnlyHint, idempotentHint and destructiveHint=false, so safety is covered. The description adds genuinely new behavioral context: the result prefers a recommended direct-dial number when multiple are on file, and the example surfaces the _apiKey auth requirement. It omits rate-limit/credit-cost behavior and what happens on a miss.

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 compact sentences: purpose first, then the identifier rule, then the preference behavior, then a runnable example. Nothing is repeated from the schema verbatim and every sentence carries distinct information.

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 read-only, open-world lookup with 100% schema coverage and no output schema, the description covers inputs, auth, and the result-selection rule. The remaining gap is failure/empty-result behavior — an agent cannot tell what happens when no phone number exists — which matters for a lookup tool with a hit-or-miss outcome.

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 baseline would be 3; the description earns above that by consolidating the alternative-identifier logic ('name + current employer (or linkedin_url / email)') into one readable rule and pairing it with a concrete invocation example including _apiKey. It adds no new detail on individual field formats, but the schema already does that.

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 — 'Find a person's phone number via RocketReach' — and immediately qualifies the identifier inputs (name + current employer, or linkedin_url, or email). No sibling tool in the list does contact lookup, so no differentiation burden exists, and an agent can tell exactly what this returns.

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 gives clear context for when the tool applies and enumerates the three accepted identifier combinations, which is the main decision an agent must make. It does not state exclusions (e.g. when not to use it, or what to do when no number is found), so it stops short of explicit when-not guidance.

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