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

Annotations already carry readOnlyHint=true, and the description reinforces this with 'sent messages (deliveries)' and a GET endpoint. It adds useful scope ('across the workspace') but does not disclose pagination/return characteristics or other behavioral traits beyond what annotations provide.

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 tight sentences: the primary action and scope are front-loaded, filters are summarized in one phrase, and the endpoint line is useful context without padding.

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 read-only, optional-parameter list tool this is nearly complete: scope, filterable fields, and endpoint are all present, and pagination/limit semantics are fully covered by the schema. The only small gap is no mention of the response envelope, and there is no output schema.

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%, and the description only echoes the filters (type/campaign/newsletter) already documented in the schema. It adds no new meaning beyond the parameter names and schema descriptions, so the 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?

Clearly states 'List sent messages (deliveries) across the workspace' – a specific verb, resource, and scope. It also names filter dimensions and the API endpoint, and 'across the workspace' distinguishes it from sibling customerio_get_customer_messages.

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 a broad workspace-level read and lists filters, so an agent can tell when a general list is intended. However, it never states when to prefer sibling tools like customerio_get_customer_messages for per-customer messages, or when not to use this tool.

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