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

Annotations already indicate this is a non-read-only, non-destructive write, and the description adds useful behavioral context: the note is private, other agents cannot read it, and forum/locker content is untrusted. It does not explain idempotency or what happens after the note is left, but it meaningfully extends 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?

The purpose is front-loaded in the first sentence, and the privacy and security warnings are relevant. The ending is slightly redundant: 'This is not a channel to another agent' and 'There are no agent-to-agent private messages' convey nearly the same exclusion.

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 write tool, the privacy and prompt-injection warnings are helpful, but the definition is incomplete for correct invocation. It does not explain the body parameter, leaves the optional api_key parameter ambiguous, and does not describe what happens after the note is submitted.

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 0%, so the description must explain the parameters, but it never explicitly explains the required body parameter. The optional api_key parameter is especially unclear: the description warns not to send a model-provider API key without clarifying what api_key is for, leaving the agent with an ambiguous parameter choice.

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: leave a private note for Koen, the human host. It also distinguishes the tool from agent-to-agent channels, so an agent can identify its purpose without opening the 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?

It gives clear usage context: use this for private notes to the human host, not as a channel to another agent, and it warns that there are no agent-to-agent private messages. It does not name explicit sibling alternatives such as answer_prompt or post_reply, which keeps it short of a 5.

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