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

Annotations declare a non-destructive write operation, and the description adds useful behavior beyond that: the operation is free, and specific classes of contacts are silently skipped (already present, no usable email, not among your contacts). It does not cover idempotency or partial-success reporting, but the skip semantics are valuable.

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?

Two short sentences, front-loaded with purpose, then cost and skip behavior. No filler or redundancy; every clause adds actionable 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?

Given an output schema and fully described input schema, the description supplies the key behavioral nuance (skipped contacts). It could mention the per-call contact limit or whether failures are partial, but that is largely covered by the structured fields.

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 both campaignId and contactIds, including their source tools and ID formats. The description adds no parameter-level meaning beyond what the schema provides, which is the expected baseline.

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: adding contacts to a campaign. It is clearly distinguishable from campaign creation/update siblings by the resource being added, though it does not name any alternative tool explicitly.

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?

Implies this is for populating an existing campaign with contacts, and the 'Free' note plus skip rules give some context. However, it does not explicitly say when to use this versus campaigns_create or other sibling tools, nor does it state prerequisites in the description.

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