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

Annotations already mark this as a non-read-only, open-world, non-destructive write. The description adds real context beyond them: the 2,000-character cap, the default per-call confirmation that can be disabled, the fact that it reaches other people (needing user confirmation), and the Cotlet API key requirement.

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?

Front-loaded with purpose, then limits and safety guidance. Slight redundancy between 'Message one guest in their message log' and 'Sends a private message to one guest', but no wasted filler.

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 mutation tool with annotations covering the safety profile and no output schema, the description supplies the character limit, confirmation behavior, external-recipient warning, and auth requirement. An agent has enough to call it correctly; only explicit alternative-tool routing is missing.

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 coverage is 100% with all three parameters documented, so the schema carries parameter meaning. The description restates the 2,000-character limit already in the message field description and adds nothing new about event_id or guest_id. Baseline 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?

States a specific verb and resource ('Sends a private message to one guest') and scopes it to a single recipient, which implicitly separates it from the sibling broadcast-style send_message. It is clear and specific, though it never names the alternative tool to sharpen the distinction.

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 operational guidance ('By default you confirm each call', 'confirm with the user before each call') but does not say when to choose this tool over paperless-post_send_message or send_invitation. Usage context is implied by the 'one guest' scope rather than stated.

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