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

Annotations cover the safety profile (readOnlyHint=false, openWorldHint=true, destructiveHint=false), and the description adds value on top: default per-call confirmation with an opt-out switch, that the message reaches other people, and that a Cotlet API key with app access is required. The duplication weakens but does not negate this added 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?

The first two sentences say the same thing ('the same as Send Message on your dashboard' appears twice), which is outright redundancy rather than brevity. The genuinely useful facts (confirmation default, API key requirement) are buried after the repeated opener.

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 write tool with no output schema, the description covers the important extras: external recipients, confirmation behavior, and credential requirements. It omits delivery/return expectations but is otherwise sufficient to call safely.

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 all three parameters are documented in the schema, so the description's note that subject and message text are required merely restates required-field information already available. Baseline 3 applies since the schema carries the parameter burden.

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?

Names a specific verb and resource (send a message to one or more clients) and grounds it in the dashboard equivalent, so an agent knows what the tool does. It does not, however, distinguish this from related Thryv siblings such as thryv_list_conversations or other messaging tools.

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 states that each call is confirmed by default (toggleable) and instructs the agent to confirm with the user before every call, which is real operational guidance. It never states when to prefer this tool over an alternative channel or which sibling handles conversations/replies.

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