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

Annotations already declare readOnlyHint, idempotentHint, openWorldHint and destructiveHint=false, so the safety profile is covered. The description adds genuinely new operational context the annotations do not: the master API key authorization requirement and the per-request cost of $0.012 for successful calls, both of which affect whether an agent should call it.

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?

The operative content is front-loaded in two short sentences with zero waste. The embedded pricing comment block is boilerplate policy noise rather than tool guidance, but it is clearly delimited and does not obscure the primary instruction.

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 not be described, and annotations cover the safety profile; the description supplies the missing auth and cost context. For a one-parameter lookup tool this is close to complete, with only the sibling-routing guidance absent.

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?

There is a single required parameter (contact_id) documented at 100% schema coverage, so the schema carries the semantics. "by ID" merely restates the parameter in prose and adds no format, sourcing, or validation detail beyond the schema's "Contact ID" description.

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?

"View a contact by ID" states a specific verb and resource, and the identifier-based lookup is unambiguous. However, the title ("Update or View Contact") contradicts the read-only framing and the description never distinguishes this tool from the sibling patch_apollo_contacts_contact_id, which is the write path for the same resource.

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 the natural usage (direct lookup by a known ID) and states the master API key prerequisite, which is a real gate. But it gives no when-to-use/when-not guidance versus siblings such as post_apollo_contacts_search (find by criteria) or patch_apollo_contacts_contact_id (modify), so routing relies on inference.

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