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

Annotations already indicate this is a write operation (readOnlyHint=false), reaches external users (openWorldHint=true), and is non-destructive. The description adds useful context: confirmation behavior, the requirement to confirm because it reaches other people, and the need for a Cotlet API key with app access.

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 core purpose is front-loaded, but the first two sentences repeat the same action, and the two confirmation statements ('By default you confirm each call; you can switch that off' and 'Reaches other people: confirm with the user before each call') could be consolidated. Several sentences earn their place, but there is noticeable redundancy.

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 two-parameter send-message tool with no output schema, the description covers the action, effect on the client, confirmation policy, and API-key prerequisite. It is largely complete, though it does not clarify the interaction between the default confirmation toggle and the separate 'reaches other people' confirmation instruction.

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%, with client_id documented as coming from list_clients and body as message text. The description does not add format, length, or syntax details beyond what the schema already provides, so 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?

States a specific verb and resource: send a message to a client in the Trainerize messenger under your name. It also scopes the action to one client and notes the client sees it in the app, distinguishing it from read-only or listing tools. The app name differentiates it from the many send_message siblings in other apps.

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?

Provides clear context: send to a client, confirmation is required by default and can be disabled, and an API key with app access is needed. It does not name alternative tools or state when-not to use this one, but the operational scenario is clear.

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