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

Annotations already declare readOnlyHint=false and destructiveHint=true, so the safety profile is covered. The description adds real-world impact ('This sends messages to real customers') and explains how behavior varies by inbox type (ongoing vs scheduled one-off), which goes beyond the annotations.

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?

Four tight sentences, front-loaded with the core action and the kind-selection logic before the exclusion and prerequisite notes. Dense but every sentence earns its place; only marginally verbose.

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 destructive, non-idempotent mutation tool with no output schema and low parameter coverage, it covers the critical context: kind semantics, prerequisites, and the fact that real messages are sent. Remaining gaps are the minor boolean/string params, which are largely self-evident.

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 low (29%), so the description carries extra burden. It does clarify inbox_id's role in determining campaign kind and explains audience/scheduled_at semantics, but title, enabled, message, and trigger_only_during_business_hours remain undocumented in both schema and 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?

States a specific verb+resource ('Create a campaign') and then disambiguates by describing the two supported campaign kinds (ongoing for website inboxes, one-off for SMS inboxes). It explicitly distinguishes itself from WhatsApp campaign tools and voice campaign siblings, so an agent can select it without opening a schema.

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?

Gives explicit routing rules: website/SMS inboxes go here, WhatsApp campaigns do not ('composed by the administrator at Campaigns -> WhatsApp'). It also names prerequisites ('Call list_inboxes and list_labels first'), leaving little to inference.

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