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

With annotations already declaring readOnlyHint=false, idempotentHint=false and destructiveHint=true, the description still adds real behavioral value: 'No email is sent by this call' discloses a side effect the annotations don't cover, and 'Returns the new user_id' plus 'POST /user' describe the mechanism and result. It does not, however, explain the destructive/auth implications the destructiveHint annotation implies.

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?

Four short, front-loaded fragments with zero filler: the write scope, the side-effect disclaimer, the return value, and the endpoint. Every clause earns its place.

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 nine-parameter write tool with no output schema, the description usefully covers the return value ('new user_id') and the no-email side effect, and the annotations handle the safety profile. It could say more about required permissions or the required customer_id, but nothing critical 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 description coverage is 100%, with all nine parameters documented in the schema itself (including the name vs first_name/last_name alternative). The description adds no parameter-level detail beyond that, so the baseline 3 applies when the schema carries the load.

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 ('add a contact (person) to an existing customer'), disambiguating from the sibling create_customer by clarifying that this creates a person, not a customer. An agent can distinguish it from chargeover_create_customer or chargeover_create_note without opening any 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?

The phrase 'to an existing customer' implies the prerequisite that the customer must already exist, and the 'WRITE:' prefix signals its place among read siblings. However, it names no alternative tools and gives no explicit when-to-use/when-not guidance, so usage is only implied.

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