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

Annotations already declare destructiveHint=true, readOnlyHint=false, idempotentHint=false and openWorldHint=true; the description goes well beyond them by stating that messages spend credits, cannot be recalled once sent, require opt-in compliance, and should be user-confirmed. It also discloses the return payload (request_id and message_id) and the underlying endpoint PUT /message.

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 critical warning ('spends credits and cannot be recalled') is front-loaded in the first clause, which is exactly right for a destructive write. The remaining sentences each carry distinct information (recipients, compliance, confirmation, tokens, return values), though the token enumeration is slightly list-like rather than prose.

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 12-parameter mutation tool, the description covers the destructive nature, credits cost, scheduling and cancellation path, compliance preconditions, mail-merge behavior, and return identifiers. With no output schema present, the 'returns request_id and message_id' note closes the main remaining gap.

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 100%, so baseline is 3; the description adds real value beyond the schema by documenting mail-merge token syntax ([$FirstName], [$LastName], [$FullName], [$CustomData-NAME]) that maps to the mail_merge_* parameters and the body fields. It does not spell out any of the other 12 parameters, but the schema covers those adequately.

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 concrete verb and resource ('send an SMS and/or an email to distribution lists or specific subscriptions') and immediately scopes the operation as a real, credit-spending, non-recallable write. It also names the related sibling trumpia_cancel_scheduled_message for the scheduling case, so an agent can distinguish this from pure read/list tools 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 explicitly covers when to use it (send now, or schedule with send_date), the alternative path for undoing a scheduled send (trumpia_cancel_scheduled_message), and the preconditions ('Subscribers must have opted in (TCPA, CAN-SPAM, CTIA)', 'Confirm the recipients and text with the user first'). The only missing routing note is against the sibling trumpia_send_sms, but the guidance is otherwise explicit.

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