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

Annotations only flag readOnly=false, openWorld=true, destructive=false; the description adds real behavioral context beyond that: messages go out under the user's name, each call is confirmed by default (and how to switch that off), the action reaches other people, and a Cotlet API key with app access is required. This is exactly the extra context annotations cannot carry.

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 purpose and appropriately short, but the reply/new-thread idea is stated twice ('New Secure Messaging thread, or a reply' then 'a reply when thread_id is set, otherwise a new thread'), and the confirmation note is also repeated. Minor redundancy keeps it from a 5.

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 messaging tool with no output schema, the description covers everything needed to call it safely: mode selection, recipient targeting, confirmation/consent requirement, and auth prerequisites. 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%, so the baseline is 3, but the description adds behavioral meaning by tying thread_id to reply-vs-new-thread behavior and explaining that 'to' targets contacts or staff for the new-thread case. It mostly restates schema content, hence not a 5.

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 (sends a Secure Messaging message) and immediately distinguishes the two modes: a reply when thread_id is set, otherwise a new thread to contacts/staff. An agent can tell exactly what operation this performs 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?

Gives a clear branching condition (thread_id present = reply, absent = new thread) and the confirmation expectation before each call. It does not name a sibling read tool (list_message_threads appears only in the schema) or state exclusions, so it stops short of a full 5.

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