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

Beyond the annotations (openWorldHint=true, destructiveHint=false), it discloses that each call is confirmed by default and that this can be switched off, and that a Cotlet API key with app access is required. The open-world/external-reach aspect is reinforced by 'Reaches other people', adding real invocation context.

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, but the first two sentences are near-duplicates ('everyone on the unsent list' / 'everyone on the unsent guest list'), and 'Guests receive it as soon as it goes out' adds little. The confirmation and auth notes are useful but the redundancy dilutes the structure.

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 two-parameter mutation with no output schema, the description covers the action, scheduling behavior, the confirmation default, and the auth requirement. An agent has enough to invoke it correctly, though it doesn't describe error or post-send state behavior.

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%, so both event_id and send_at are fully documented in the schema. The description restates the send_at behavior ('scheduled instead of sent now') without adding format or syntax detail beyond what the schema already provides, 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 (Card/Flyer/invitation) with an explicit scope: everyone on the unsent guest list. This scope distinguishes it from siblings like send_message and send_private_message, which target individual recipients.

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?

Conveys when to use it (to dispatch to the unsent list) and notes the send_at variant for scheduling rather than immediate sending. It stops short of naming alternative tools for messaging subsets of guests, so the routing guidance is clear but not exhaustive.

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