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

With annotations covering safety (readOnlyHint=false, destructiveHint=false, openWorldHint=true), the description still adds substantial context: the payment_required failure mode, the default per-call confirmation with an opt-out, the fact that it reaches external people, and the API key/access requirement. This is exactly the behavioral detail annotations cannot express.

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-loads the core action, then layers constraints. Minor redundancy: 'Free designs only' and 'It works for free invitations' restate the same point, and confirmation is mentioned twice ('By default you confirm each call' and 'confirm with the user before each call'). Otherwise every sentence carries information.

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 single-parameter sending tool with no output schema, the description covers everything an agent needs: scope, payment limits and the payment_required stop, confirmation policy, external reach, and auth requirements. Nothing material 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% and the single parameter (event_id) is already documented in the schema as 'Event ID from list_events.' The description adds no additional meaning about the parameter, so the 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 (send) and resource (draft invitation) with scope qualifiers: 'to its guests', 'Free designs only', and 'every guest on its list'. This distinguishes it clearly from siblings like evite_message_guests or evite_add_guests, though it does not name any sibling explicitly.

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 a clear when-to-use condition ('Free designs only', 'works for free invitations') and a when-not with the resulting behavior (Premium invitations stop with payment_required and must be finished in Evite). Strong routing guidance, though it does not name an alternative tool to call instead.

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