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

Annotations already declare a safe read (readOnlyHint=true, destructiveHint=false), but the description adds substantial context beyond them: the paid-plan requirement, the 403 failure mode on free plans, BYOK key passing, the 0-credit cost, and critically the obfuscated output (last name obscured, no email or phone). These are exactly the behavioral traits an agent needs before calling.

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?

Front-loaded with the most disqualifying constraint (paid plan / 403) and then the routing advice, so the important facts come first. It is dense and packs several clauses, but nearly every sentence carries actionable information rather than 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?

For an 11-parameter, read-only tool with no output schema, the description covers the key gaps: plan/access prerequisites, authentication model, cost, and the shape and limitations of the returned data. An agent has enough to decide and invoke correctly without more.

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 11 parameters thoroughly, and the inline example largely duplicates the schema's own examples. The description adds the BYOK note about _apiKey, but contributes little else beyond what the structured schema provides – 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 and resource ("Search Apollo's people database") and narrows the scope by the fields it searches on (job title, seniority, employer domain/org id). It is clearly distinguishable from apollo_enrich_person and apollo_search_organizations, which are named or implied in the surrounding text.

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?

Explicitly routes the agent: use this to search, but call apollo_enrich_person on a result to resolve a real contact, because this endpoint returns obfuscated last names and no email/phone. It also states a hard prerequisite (PAID plan; free plan returns 403), giving a clear when-to-use and when-not-to-use signal.

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