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

Annotations already declare destructiveHint=true, idempotentHint=false, and openWorldHint=true, so the mutation/safety profile is covered structurally. The description adds the auth requirement (master API key) and pricing, which is real context, but it never explains the consequence of the destructive hint (e.g., contacts entering an outbound sequence) that the annotations imply.

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 functional sentence is front-loaded and waste-free, and the auth requirement follows immediately. The embedded pricing comment block is boilerplate noise but is clearly demarcated and does not obscure the core 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?

With a full output schema and 100% parameter coverage, return values and inputs are covered, so the remaining burden is behavioral. For a destructive 11-parameter mutation the description is minimally adequate: it names the auth requirement but omits consequences, conflict conditions with the remove/stop sibling, and how the several 'allow contacts with...' flags interact.

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 all 11 parameters including contact_ids/label_names alternation are documented in the schema itself. The description adds nothing about parameter semantics, so the 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?

The description states a specific verb and resource ('Add contacts to a sequence'), which an agent can map directly to the operation. It does not, however, differentiate itself from the closely named sibling post_apollo_emailer_campaigns_remove_or_stop_contact_ids or explain the contact/label ambiguity that the schema raises.

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?

There is no when-to-use guidance, no conditions distinguishing adding from removing/stopping contacts, and no note on prerequisites beyond 'Requires a master API key.' The agent is left to infer when this tool is the correct choice vs. siblings like the remove/stop variant or sequence approve/abort.

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