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

Annotations already declare readOnlyHint=true, but the description adds meaningful context beyond that: it explicitly rules out sending campaigns from this server, which is a genuinely useful behavioral boundary an agent could otherwise get wrong. It also discloses page-based pagination. It stops short of describing result size, ordering, or error behavior.

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 short, front-loaded statements with no filler; the key scoping fact (read-only, does not send) appears early. The trailing 'MailerLite API: GET /campaigns' is marginally useful for grounding the endpoint but is the least load-bearing sentence, keeping this just shy of a 5.

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 simple three-parameter, zero-required list tool with full schema coverage and readOnlyHint already set, the description covers purpose, pagination, safe-read behavior, and the send boundary. With no output schema present, nothing further is strictly needed for an agent to call this correctly.

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 schema already documents page semantics, the default limit of 25, and the status enum values with the underlying filter[status] mapping. The description only restates pagination and status filtering at a high level, adding no syntax or format detail beyond the schema, so the baseline of 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 ('List campaigns') and adds a scope clarification ('this server does NOT send campaigns'), which separates it from send-oriented operations. It does not, however, explicitly contrast itself with the closest sibling, mailerlite_get_campaign (single vs. collection), so sibling differentiation is only partial.

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?

'Optionally filtered by status' implies the usage context for the filter parameter, and the read-only note implies when to reach for this tool. There is no explicit when-to-use or when-not-to-use guidance, nor any routing to mailerlite_get_campaign for a single campaign, so usage is only implied.

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