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

Annotations are limited (readOnlyHint=false, openWorldHint=true, destructiveHint=false), and the description adds substantial context: nothing is sent to the guest so no confirmation is required, the return value is the new guest_id, a plus-one becomes a second guest in the same party, and a Cotlet API key with app access is required. These are behavioral facts annotations cannot convey.

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 the core action and the no-notification constraint, and every sentence is functional. Slightly redundant, restating 'nothing is sent' as both 'Nothing is sent to the guest' and 'Nothing is sent to anyone'.

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 no output schema, the description covers side effects, return value, plus-one semantics, auth requirements, and the sibling used for events. An agent has everything needed to call it 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 coverage is already 100%, so the baseline is 3. The description still adds meaning beyond the schema by explaining the semantic effect of plus_one (added as a separate guest in the same party) and the list placement choices, which clarifies how the parameters behave.

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 (add a guest, optionally with a plus-one, to your guest list) and names the sibling action for a related task (invite_guest_to_event). An agent can distinguish this from list_guests or invite_guest_to_event without opening a 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?

Gives clear context: adds to 'Definitely Invited' or 'Maybe', nothing is sent, so it runs without asking first, and events are handled separately via invite_guest_to_event. Strong routing guidance, though no explicit when-not conditions.

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