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

The description carries the non-obvious behavioral fact that the tool returns step-by-step UI instructions (screens, buttons, fields) and 'opens nothing by itself', which is exactly the kind of context annotations cannot express and which is consistent with readOnlyHint=true. It could go further on what happens if the user has no Mailjet session or Cloud Browser open, but the key trait is disclosed.

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 first two sentences are front-loaded and earn their place, correctively stating what the tool does and how to complete the action. The closing sentence about Mailjet's REST API and read-only MCP server, including a 'checked 22 Oct 2026' date, is background trivia that does not help an agent call this tool and dilutes the message.

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 zero parameters, no output schema, and annotations covering the safety profile, what remains is explaining the return value and the follow-on action — both of which the description covers. The gap is limited to workflow prerequisites (existing Cloud Browser session, account state) and the absence of any explicit sibling routing.

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?

The tool takes zero parameters and the schema is an empty closed object, so there is nothing for the description to disambiguate beyond what it already says about needing the user's own Mailjet account. Baseline 4 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?

States a specific verb+resource ('Schedule campaign') and immediately qualifies that it returns instructions rather than performing the action, which prevents the most likely misread. It does not explicitly contrast with siblings like mailjet_send_campaign or mailjet_update_campaign_subject, so the boundary is clear but not fully differentiated.

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?

It gives a clear follow-up path — 'then do it with the cotlet_browser_* tools in the user's Mailjet Cloud Browser' — which is genuine when-to-use guidance. However, it never says when to pick this over the adjacent mailjet_* campaign tools (send, update subject, duplicate), so the agent must infer the boundary from names alone.

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