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

Annotations already carry readOnlyHint, idempotentHint, and destructiveHint, so the description does not need to restate them. The description adds a useful precondition, the Sales Navigator subscription requirement, and clarifies that it acts on an existing thread. It does not expand on side effects such as recipient delivery, CRM copying beyond the schema, or irreversibility, so coverage is adequate but not rich.

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?

Two short sentences: the first immediately states what the tool does and the second gives the two key usage conditions. It is front-loaded and contains no filler or irrelevant detail.

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?

Given the complete parameter schema, existing output schema, and non-contradictory annotations, the description covers the essential preconditions and source of the thread ID. It is slightly thin on explicit exclusions and side-effect context, but nothing needed to make a correct call is clearly 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?

The input schema already documents all 5 parameters with 100% description coverage, so the description does not need to carry the full parameter burden. It adds value by instructing where to get the thread_id from, but it does not add meaning to the other parameters like text, account_id, copy_to_crm, or idempotency_key beyond what the schema already provides.

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 specific verb and resource: send a message in an existing Sales Navigator thread. It also includes the internal action name and makes clear this is the Sales Navigator messaging path rather than generic LinkedIn messaging, so it is distinguishable from its siblings.

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 clearly gives context for when this tool is usable: an existing Sales Navigator thread, an account with a Sales Navigator subscription, and the thread ID from salesnav_list_messaging_threads. It does not explicitly enumerate exclusions or direct users to a generic alternative like send_message, but the necessary usage context is clear.

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